diff --git a/include/tradstdc.h b/include/tradstdc.h
index c5a9368fb..b607d4a99 100644
--- a/include/tradstdc.h
+++ b/include/tradstdc.h
@@ -327,13 +327,20 @@ typedef genericptr genericptr_t; /* (void *) or (char *) */
 /*
  * Give first priority to standard
  */
-#ifndef ATTRNORETURN
 #if defined(__STDC_VERSION__) || defined(__cplusplus)
 #if (__STDC_VERSION__ > 202300L) || defined(__cplusplus)
+#ifndef ATTRNORETURN
 #define ATTRNORETURN [[noreturn]]
 #endif
-#endif
-#endif
+#ifndef __has_c_attribute
+#define __has_c_attribute(x) 0
+#endif /* __has_c_attribute */
+#if __has_c_attribute(fallthrough)
+/* Standard attribute is available, use it. */
+#define FALLTHROUGH [[fallthrough]]
+#endif  /* __has_c_attribute(fallthrough) */
+#endif  /* __STDC_VERSION__ gt 202300L || __cplusplus */
+#endif  /* __STDC_VERSION || __cplusplus */
 
 /*
  * Allow gcc2 to check parameters of printf-like calls with -Wformat;
@@ -366,12 +373,21 @@ typedef genericptr genericptr_t; /* (void *) or (char *) */
 #endif  /* !NONNULLS_DEFINED */
 /* #pragma message is available */
 #define NH_PRAGMA_MESSAGE 1
-#endif
-#endif
+#endif  /* __GNUC__ greater than or equal to 5 */
+#endif  /* __GNUC__ */
 
-#if defined(__clang__) && !defined(DO_DEFINE_NONNULLS)
+#if defined(__clang__)
+#ifndef FALLTHROUGH
+#if defined(__clang_major__)
+#if __clang_major__ >= 9
+#define FALLTHROUGH __attribute__((fallthrough))
+#endif  /* __clang_major__ greater than or equal to 9 */
+#endif  /* __clang_major__ is defined */
+#endif  /* FALLTHROUGH */
+#if !defined(DO_DEFINE_NONNULLS)
 #define DO_DEFINE_NONNULLS
 #endif
+#endif  /* __clang__ */
 
 #if defined(DO_DEFINE_NONNULLS) && !defined(NONNULLS_DEFINED)
 #define NONNULL __attribute__((returns_nonnull))
@@ -405,6 +421,7 @@ typedef genericptr genericptr_t; /* (void *) or (char *) */
 #define NH_PRAGMA_MESSAGE 1
 #endif
 
+/* Fallback implementations */
 #ifndef PRINTF_F
 #define PRINTF_F(f, v)
 #endif
@@ -414,6 +431,9 @@ typedef genericptr genericptr_t; /* (void *) or (char *) */
 #ifndef UNUSED
 #define UNUSED
 #endif
+#ifndef FALLTHROUGH
+#define FALLTHROUGH
+#endif
 #ifndef ATTRNORETURN
 #define ATTRNORETURN
 #endif
diff --git a/src/allmain.c b/src/allmain.c
index 4d281fe7f..253ac82a4 100644
--- a/src/allmain.c
+++ b/src/allmain.c
@@ -1040,6 +1040,7 @@ argcheck(int argc, char *argv[], enum earlyarg e_arg)
                 extended_opt++;
                 return windows_early_options(extended_opt);
             }
+        FALLTHROUGH;
         /*FALLTHRU*/
 #endif
         default:
diff --git a/src/apply.c b/src/apply.c
index 271a6cd18..6f1112359 100644
--- a/src/apply.c
+++ b/src/apply.c
@@ -3772,6 +3772,7 @@ use_grapple(struct obj *obj)
             (void) thitmonst(mtmp, uwep);
             return ECMD_TIME;
         }
+        FALLTHROUGH;
     /*FALLTHRU*/
     case 3: /* Surface */
         if (IS_AIR(levl[cc.x][cc.y].typ) || is_pool(cc.x, cc.y))
@@ -3891,6 +3892,7 @@ do_break_wand(struct obj *obj)
             discard_broken_wand();
             return ECMD_TIME;
         }
+        FALLTHROUGH;
         /*FALLTHRU*/
     case WAN_WISHING:
     case WAN_NOTHING:
@@ -3919,6 +3921,7 @@ do_break_wand(struct obj *obj)
         Soundeffect(se_wall_of_force, 65);
         pline("A wall of force smashes down around you!");
         dmg = d(1 + obj->spe, 6); /* normally 2d12 */
+        FALLTHROUGH;
         /*FALLTHRU*/
     case WAN_CANCELLATION:
     case WAN_POLYMORPH:
@@ -4304,6 +4307,7 @@ doapply(void)
             pline("It rings! ... But no-one answers.");
             break;
         }
+        FALLTHROUGH;
         /*FALLTHRU*/
     default:
         /* Pole-weapons can strike at a distance */
diff --git a/src/ball.c b/src/ball.c
index c3c53c289..d6ba11017 100644
--- a/src/ball.c
+++ b/src/ball.c
@@ -743,7 +743,8 @@ drag_ball(coordxy x, coordxy y, int *bc_control,
                     SKIP_TO_DRAG;
                 break;
             }
-        /* fall through */
+	    FALLTHROUGH;
+        /* FALLTHRU */
         case 1:
         case 0:
             /* do nothing if possible */
diff --git a/src/dbridge.c b/src/dbridge.c
index 8e2f081bd..5e739d4fa 100644
--- a/src/dbridge.c
+++ b/src/dbridge.c
@@ -255,6 +255,7 @@ create_drawbridge(coordxy x, coordxy y, int dir, boolean flag)
         break;
     default:
         impossible("bad direction in create_drawbridge");
+        FALLTHROUGH;
         /*FALLTHRU*/
     case DB_WEST:
         horiz = FALSE;
diff --git a/src/display.c b/src/display.c
index 9902040a2..0e9cca612 100644
--- a/src/display.c
+++ b/src/display.c
@@ -528,6 +528,7 @@ display_monster(
         default:
             impossible("display_monster:  bad m_ap_type value [ = %d ]",
                        (int) mon->m_ap_type);
+            FALLTHROUGH;
             /*FALLTHRU*/
         case M_AP_NOTHING:
             show_glyph(x, y, mon_to_glyph(mon, newsym_rn2));
@@ -3566,6 +3567,7 @@ wall_angle(struct rm *lev)
     case SDOOR:
         if (lev->horizontal)
             goto horiz;
+        FALLTHROUGH;
         /*FALLTHRU*/
     case VWALL:
         switch (lev->wall_info & WM_MASK) {
diff --git a/src/do.c b/src/do.c
index f4f7c3e4d..fe07407c1 100644
--- a/src/do.c
+++ b/src/do.c
@@ -2217,6 +2217,7 @@ revive_corpse(struct obj *corpse)
                 fill_pit(mtmp->mx, mtmp->my);
                 break;
             }
+            FALLTHROUGH;
             /*FALLTHRU*/
         default:
             /* we should be able to handle the other cases... */
diff --git a/src/do_name.c b/src/do_name.c
index aa4463cda..d1d53f36e 100644
--- a/src/do_name.c
+++ b/src/do_name.c
@@ -442,6 +442,7 @@ objtyp_is_callable(int i)
            determine which one was the real one */
         if (i == AMULET_OF_YENDOR || i == FAKE_AMULET_OF_YENDOR)
             break; /* return FALSE */
+        FALLTHROUGH;
         /*FALLTHRU*/
     case SCROLL_CLASS:
     case POTION_CLASS:
diff --git a/src/do_wear.c b/src/do_wear.c
index e7cc1be64..1b5b57dfd 100644
--- a/src/do_wear.c
+++ b/src/do_wear.c
@@ -452,6 +452,7 @@ Helmet_on(void)
                          : (uarmh->o_id % 2) ? A_CHAOTIC : A_LAWFUL,
                      A_CG_HELM_ON);
         /* makeknown(HELM_OF_OPPOSITE_ALIGNMENT); -- below, after Tobjnam() */
+        FALLTHROUGH;
     /*FALLTHRU*/
     case DUNCE_CAP:
         if (uarmh && !uarmh->cursed) {
diff --git a/src/dog.c b/src/dog.c
index 9c4f85560..6134355f9 100644
--- a/src/dog.c
+++ b/src/dog.c
@@ -523,7 +523,9 @@ mon_arrive(struct monst *mtmp, int when)
         } else if (!(u.uevent.qexpelled
                      && (Is_qstart(&u.uz0) || Is_qstart(&u.uz)))) {
             impossible("mon_arrive: no corresponding portal?");
-        } /*FALLTHRU*/
+        }
+        FALLTHROUGH;
+        /*FALLTHRU*/
     default:
     case MIGR_RANDOM:
         xlocale = ylocale = 0;
@@ -1076,6 +1078,7 @@ dogfood(struct monst *mon, struct obj *obj)
             && obj->oclass != BALL_CLASS
             && obj->oclass != CHAIN_CLASS)
             return APPORT;
+        FALLTHROUGH;
         /*FALLTHRU*/
     case ROCK_CLASS:
         return UNDEF;
diff --git a/src/dogmove.c b/src/dogmove.c
index 2c77a6487..29c0d9bc1 100644
--- a/src/dogmove.c
+++ b/src/dogmove.c
@@ -76,6 +76,7 @@ droppables(struct monst *mon)
             if (pickaxe && pickaxe->otyp == PICK_AXE && pickaxe != wep
                 && (!pickaxe->oartifact || obj->oartifact))
                 return pickaxe; /* drop the one we earlier decided to keep */
+            FALLTHROUGH;
         /*FALLTHRU*/
         case PICK_AXE:
             if (!pickaxe || (obj->oartifact && !pickaxe->oartifact)) {
@@ -104,12 +105,14 @@ droppables(struct monst *mon)
             if (key && key->otyp == LOCK_PICK
                 && (!key->oartifact || obj->oartifact))
                 return key; /* drop the one we earlier decided to keep */
+            FALLTHROUGH;
         /*FALLTHRU*/
         case LOCK_PICK:
             /* keep lock-pick in preference to credit card */
             if (key && key->otyp == CREDIT_CARD
                 && (!key->oartifact || obj->oartifact))
                 return key;
+            FALLTHROUGH;
         /*FALLTHRU*/
         case CREDIT_CARD:
             if (!key || (obj->oartifact && !key->oartifact)) {
diff --git a/src/dokick.c b/src/dokick.c
index b9d25eaaf..cf8bb405b 100644
--- a/src/dokick.c
+++ b/src/dokick.c
@@ -1340,6 +1340,7 @@ dokick(void)
                 pline("%s burps loudly.", Monnam(u.ustuck));
                 break;
             }
+            FALLTHROUGH;
             /*FALLTHRU*/
         default:
             Your("feeble kick has no effect.");
@@ -1484,6 +1485,7 @@ drop_to(coord *cc, schar loc, coordxy x, coordxy y)
             cc->y = cc->x = 0;
             break;
         }
+        FALLTHROUGH;
         /*FALLTHRU*/
     case MIGR_STAIRS_UP:
     case MIGR_LADDER_UP:
@@ -1800,6 +1802,7 @@ obj_delivery(boolean near_hero)
         switch (where) {
         case MIGR_LADDER_UP:
             isladder = TRUE;
+            FALLTHROUGH;
             /*FALLTHRU*/
         case MIGR_STAIRS_UP:
         case MIGR_SSTAIRS:
diff --git a/src/dothrow.c b/src/dothrow.c
index 30af1e40b..7dcf043f9 100644
--- a/src/dothrow.c
+++ b/src/dothrow.c
@@ -67,6 +67,7 @@ multishot_class_bonus(
     case PM_NINJA:
         if (skill == -P_SHURIKEN || skill == -P_DART)
             multishot++;
+        FALLTHROUGH;
         /*FALLTHRU*/
     case PM_SAMURAI:
         /* role-specific launcher and its ammo */
@@ -175,6 +176,7 @@ throw_obj(struct obj *obj, int shotlimit)
         switch (P_SKILL(weapon_type(obj))) {
         case P_EXPERT:
             multishot++;
+            FALLTHROUGH;
         /*FALLTHRU*/
         case P_SKILLED:
             if (!weakmultishot)
@@ -1295,6 +1297,7 @@ toss_up(struct obj *obj, boolean hitsroof)
                     Your("%s fails to protect you.", helm_simple_name(uarmh));
                 goto petrify;
             }
+            FALLTHROUGH;
             /*FALLTHRU*/
         case CREAM_PIE:
         case BLINDING_VENOM:
@@ -2572,12 +2575,14 @@ breakmsg(struct obj *obj, boolean in_view)
     default: /* glass or crystal wand */
         if (obj->oclass != WAND_CLASS)
             impossible("breaking odd object (%d)?", obj->otyp);
+        FALLTHROUGH;
         /*FALLTHRU*/
     case LENSES:
     case MIRROR:
     case CRYSTAL_BALL:
     case EXPENSIVE_CAMERA:
         to_pieces = " into a thousand pieces";
+        FALLTHROUGH;
     /*FALLTHRU*/
     case POT_WATER: /* really, all potions */
         if (!in_view)
diff --git a/src/dungeon.c b/src/dungeon.c
index e75808a31..dc8557ed4 100644
--- a/src/dungeon.c
+++ b/src/dungeon.c
@@ -3039,6 +3039,7 @@ count_feat_lastseentyp(
         }
         if (is_drawbridge_wall(x, y) < 0)
             break;
+        FALLTHROUGH;
         /*FALLTHRU*/
     case DBWALL:
     case DRAWBRIDGE_DOWN:
diff --git a/src/eat.c b/src/eat.c
index e2c369ae8..a73cf2080 100644
--- a/src/eat.c
+++ b/src/eat.c
@@ -848,6 +848,7 @@ cprefx(int pm)
             make_slimed(10L, (char *) 0);
             delayed_killer(SLIMED, KILLED_BY_AN, "");
         }
+        FALLTHROUGH;
     /* Fall through */
     default:
         if (acidic(&mons[pm]) && Stoned)
@@ -1164,19 +1165,23 @@ cpostfx(int pm)
             HSee_invisible |= FROMOUTSIDE;
         }
         newsym(u.ux, u.uy);
+        FALLTHROUGH;
         /*FALLTHRU*/
     case PM_YELLOW_LIGHT:
     case PM_GIANT_BAT:
         make_stunned((HStun & TIMEOUT) + 30L, FALSE);
+        FALLTHROUGH;
         /*FALLTHRU*/
     case PM_BAT:
         make_stunned((HStun & TIMEOUT) + 30L, FALSE);
         break;
     case PM_GIANT_MIMIC:
         tmp += 10;
+        FALLTHROUGH;
         /*FALLTHRU*/
     case PM_LARGE_MIMIC:
         tmp += 20;
+        FALLTHROUGH;
         /*FALLTHRU*/
     case PM_SMALL_MIMIC:
         tmp += 20;
@@ -1278,6 +1283,7 @@ cpostfx(int pm)
         } else {
             pline("For some reason, that tasted bland.");
         }
+        FALLTHROUGH;
     /*FALLTHRU*/
     default:
         check_intrinsics = TRUE;
@@ -2143,6 +2149,7 @@ fprefx(struct obj *otmp)
             break;
         }
         iter_mons(garlic_breath);
+        FALLTHROUGH;
         /*FALLTHRU*/
     default:
         if (otmp->otyp == SLIME_MOLD && !otmp->cursed
diff --git a/src/engrave.c b/src/engrave.c
index 8105efeec..88ac6b29e 100644
--- a/src/engrave.c
+++ b/src/engrave.c
@@ -606,6 +606,7 @@ doengrave_sfx_item_WAN(struct _doengrave_ctx *de)
                    "A few ice cubes drop from the wand.");
         if (!de->oep || (de->oep->engr_type != BURN))
             break;
+        FALLTHROUGH;
         /*FALLTHRU*/
     case WAN_CANCELLATION:
     case WAN_MAKE_INVISIBLE:
@@ -706,6 +707,7 @@ doengrave_sfx_item(struct _doengrave_ctx *de)
             de->type = DUST;
             break;
         }
+        FALLTHROUGH;
         /*FALLTHRU*/
     /* Objects too large to engrave with */
     case BALL_CLASS:
diff --git a/src/fountain.c b/src/fountain.c
index 1d4150630..979bb0518 100644
--- a/src/fountain.c
+++ b/src/fountain.c
@@ -359,6 +359,7 @@ drinkfountain(void)
                 dofindgem();
                 break;
             }
+            FALLTHROUGH;
             /*FALLTHRU*/
         case 28: /* Water Nymph */
             dowaternymph();
@@ -486,6 +487,7 @@ dipfountain(struct obj *obj)
             dofindgem();
             break;
         }
+        FALLTHROUGH;
         /*FALLTHRU*/
     case 25: /* Water gushes forth */
         dogushforth(FALSE);
@@ -699,6 +701,7 @@ drinksink(void)
             pline("From the murky drain, a hand reaches up... --oops--");
             break;
         }
+        FALLTHROUGH;
         /*FALLTHRU*/
     default:
         You("take a sip of %s %s.",
@@ -770,6 +773,7 @@ dipsink(struct obj *obj)
             try_call = TRUE;
             break;
         }
+        FALLTHROUGH;
         /* FALLTHRU */
     case POT_GAIN_LEVEL:
     case POT_GAIN_ENERGY:
diff --git a/src/getpos.c b/src/getpos.c
index 0152fba53..36e9d95ea 100644
--- a/src/getpos.c
+++ b/src/getpos.c
@@ -465,6 +465,7 @@ gather_locs_interesting(coordxy x, coordxy y, int gloc)
     case GLOC_VALID:
         if (getpos_getvalid)
             return (*getpos_getvalid)(x, y);
+        FALLTHROUGH;
         /*FALLTHRU*/
     case GLOC_INTERESTING:
         return (gather_locs_interesting(x, y, GLOC_DOOR)
diff --git a/src/hack.c b/src/hack.c
index 1f66f813b..6f8cce1d1 100644
--- a/src/hack.c
+++ b/src/hack.c
@@ -571,6 +571,7 @@ moverock_core(coordxy sx, coordxy sy)
                         dopush(sx, sy, rx, ry, otmp, costly);
                         continue;
                     }
+                    FALLTHROUGH;
                     /*FALLTHRU*/
                 case TELEP_TRAP:
                     rock_disappear_msg(otmp);
@@ -2553,6 +2554,7 @@ escape_from_sticky_mon(coordxy x, coordxy y)
                     u.ustuck->mfrozen = 1;
                     u.ustuck->msleeping = 0;
                 }
+                FALLTHROUGH;
                 /*FALLTHRU*/
             default:
                 if (u.ustuck->mtame && !Conflict && !u.ustuck->mconf)
@@ -3573,6 +3575,7 @@ check_special_room(boolean newlev)
         }
         case TEMPLE:
             intemple(roomno + ROOMOFFSET);
+            FALLTHROUGH;
         /*FALLTHRU*/
         default:
             msg_given = (rt == TEMPLE || rt >= SHOPBASE);
@@ -4317,6 +4320,7 @@ spot_checks(coordxy x, coordxy y, schar old_typ)
     switch (old_typ) {
     case DRAWBRIDGE_UP:
         db_ice_now = ((levl[x][y].drawbridgemask & DB_UNDER) == DB_ICE);
+        FALLTHROUGH;
         /*FALLTHRU*/
     case ICE:
         if ((new_typ != old_typ)
diff --git a/src/insight.c b/src/insight.c
index 7a04f4efe..c1e17e954 100644
--- a/src/insight.c
+++ b/src/insight.c
@@ -1968,6 +1968,8 @@ attributes_enlightenment(
             switch (u.umortality) {
             case 0:
                 impossible("dead without dying?");
+                FALLTHROUGH;
+                /* FALLTHRU */
             case 1:
                 break; /* just "are dead" */
             default:
@@ -2624,6 +2626,7 @@ vanqsort_cmp(
             res = uniq2 - uniq1;
             break;
         } /* else both unique or neither unique */
+        FALLTHROUGH;
         /*FALLTHRU*/
     case VANQ_ALPHA_MIX:
         name1 = mons[indx1].pmnames[NEUTRAL];
diff --git a/src/invent.c b/src/invent.c
index 1e375fc66..be0dff2cc 100644
--- a/src/invent.c
+++ b/src/invent.c
@@ -2463,6 +2463,7 @@ askchain(
         switch (sym) {
         case 'a':
             allflag = 1;
+            FALLTHROUGH;
             /*FALLTHRU*/
         case 'y':
             tmp = (*fn)(otmp);
@@ -2481,10 +2482,13 @@ askchain(
             cnt += tmp;
             if (--mx == 0)
                 goto ret;
+            FALLTHROUGH;
             /*FALLTHRU*/
         case 'n':
             if (nodot)
                 dud++;
+            FALLTHROUGH;
+            /*FALLTHRU*/
         default:
             break;
         case 'q':
@@ -2975,6 +2979,7 @@ itemactions_pushkeys(struct obj *otmp, int act)
         switch (act) {
         default:
             impossible("Unknown item action");
+            break;
         case IA_NONE:
             break;
         case IA_UNWIELD:
diff --git a/src/makemon.c b/src/makemon.c
index 947a8884d..e8c6bf298 100644
--- a/src/makemon.c
+++ b/src/makemon.c
@@ -521,6 +521,7 @@ m_initweap(struct monst *mtmp)
          */
         if (!is_demon(ptr))
             break;
+        FALLTHROUGH;
         /*FALLTHRU*/
     default:
         /*
@@ -704,12 +705,15 @@ m_initinv(struct monst *mtmp)
             /* MAJOR fall through ... */
             case 0:
                 (void) mongets(mtmp, WAN_MAGIC_MISSILE);
+                FALLTHROUGH;
                 /*FALLTHRU*/
             case 1:
                 (void) mongets(mtmp, POT_EXTRA_HEALING);
+                FALLTHROUGH;
                 /*FALLTHRU*/
             case 2:
                 (void) mongets(mtmp, POT_HEALING);
+                FALLTHROUGH;
                 /*FALLTHRU*/
             case 3:
                 (void) mongets(mtmp, WAN_STRIKING);
diff --git a/src/mcastu.c b/src/mcastu.c
index 8c28b2507..a968d7e0a 100644
--- a/src/mcastu.c
+++ b/src/mcastu.c
@@ -84,6 +84,7 @@ choose_magic_spell(int spellval)
     case 23:
         if (Antimagic || Hallucination)
             return MGC_PSI_BOLT;
+        FALLTHROUGH;
         /*FALLTHRU*/
     case 22:
     case 21:
@@ -138,6 +139,7 @@ choose_clerical_spell(int spellnum)
     case 14:
         if (rn2(3))
             return CLC_OPEN_WOUNDS;
+        FALLTHROUGH;
         /*FALLTHRU*/
     case 13:
         return CLC_GEYSER;
diff --git a/src/mhitm.c b/src/mhitm.c
index 2473c1417..f54dc4ad2 100644
--- a/src/mhitm.c
+++ b/src/mhitm.c
@@ -405,6 +405,7 @@ mattackm(
                     mswingsm(magr, mdef, mwep);
                 tmp += hitval(mwep, mdef);
             }
+            FALLTHROUGH;
             /*FALLTHRU*/
         case AT_CLAW:
         case AT_KICK:
@@ -683,6 +684,7 @@ hitmm(
                     Snprintf(buf, sizeof buf, "%s squeezes", magr_name);
                     break;
                 }
+                FALLTHROUGH;
                 /*FALLTHRU*/
             default:
                 if (!weaponhit || !mwep || !mwep->oartifact)
diff --git a/src/mkmaze.c b/src/mkmaze.c
index c1e2b6205..2aa526ce0 100644
--- a/src/mkmaze.c
+++ b/src/mkmaze.c
@@ -588,6 +588,7 @@ fixup_special(void)
                 sp = find_level(r->rname.str);
                 lev = sp->dlevel;
             }
+            FALLTHROUGH;
             /*FALLTHRU*/
 
         case LR_UPSTAIR:
@@ -2073,6 +2074,7 @@ mv_bubble(struct bubble *b, coordxy dx, coordxy dy, boolean ini)
         break;
     case 3:
         b->dy = -b->dy;
+        FALLTHROUGH;
         /*FALLTHRU*/
     case 2:
         b->dx = -b->dx;
diff --git a/src/mkobj.c b/src/mkobj.c
index 73126264e..8a9be1e0d 100644
--- a/src/mkobj.c
+++ b/src/mkobj.c
@@ -325,6 +325,7 @@ mkbox_cnts(struct obj *box)
             n = 0;
             break;
         }
+        FALLTHROUGH;
         /*FALLTHRU*/
     case BAG_OF_HOLDING:
         n = 1;
@@ -999,6 +1000,7 @@ mksobj_init(struct obj *otmp, boolean artif)
         case LARGE_BOX:
             otmp->olocked = !!(rn2(5));
             otmp->otrapped = !(rn2(10));
+            FALLTHROUGH;
             /*FALLTHRU*/
         case ICE_BOX:
         case SACK:
@@ -1184,6 +1186,7 @@ mksobj(int otyp, boolean init, boolean artif)
             if (svm.mvitals[otmp->corpsenm].mvflags & (G_NOCORPSE | G_GONE))
                 otmp->corpsenm = gu.urole.mnum;
         }
+        FALLTHROUGH;
         /*FALLTHRU*/
     case STATUE:
     case FIGURINE:
@@ -1197,6 +1200,7 @@ mksobj(int otyp, boolean init, boolean artif)
                            : is_male(ptr) ? CORPSTAT_MALE
                              : rn2(2) ? CORPSTAT_FEMALE : CORPSTAT_MALE);
         }
+        FALLTHROUGH;
         /*FALLTHRU*/
     case EGG:
     /* case TIN: */
@@ -1210,6 +1214,7 @@ mksobj(int otyp, boolean init, boolean artif)
         break;
     case POT_OIL:
         otmp->age = MAX_OIL_IN_FLASK; /* amount of oil */
+        FALLTHROUGH;
         /*FALLTHRU*/
     case POT_WATER: /* POTION_CLASS */
         otmp->fromsink = 0; /* overloads corpsenm, which was set to NON_PM */
@@ -2982,6 +2987,7 @@ objlist_sanity(struct obj *objlist, int wheretype, const char *mesg)
                 /* note: ball and chain can also be OBJ_FREE, but not across
                    turns so this sanity check shouldn't encounter that */
                 bc_ok = TRUE;
+            FALLTHROUGH;
             /*FALLTHRU*/
             default:
                 if ((obj != uchain && obj != uball) || !bc_ok) {
diff --git a/src/mon.c b/src/mon.c
index 1c2ecad07..69d206065 100644
--- a/src/mon.c
+++ b/src/mon.c
@@ -861,7 +861,6 @@ make_corpse(struct monst *mtmp, unsigned int corpseflags)
     case PM_PAGE: case PM_ABBOT: case PM_ACOLYTE: case PM_HUNTER:
     case PM_THUG: case PM_NINJA: case PM_ROSHI: case PM_GUIDE:
     case PM_WARRIOR: case PM_APPRENTICE:
-    /*FALLTHRU*/
 #else
     default:
 #endif
@@ -3076,7 +3075,8 @@ mondead(struct monst *mtmp)
                 (void) makemon(mtmp->data, stway->sx, stway->sy, NO_MM_FLAGS);
                 break;
             }
-            /* fall-through */
+	    FALLTHROUGH;
+            /* FALLTHRU */
         case 2: /* randomly */
             (void) makemon(mtmp->data, 0, 0, NO_MM_FLAGS);
             break;
@@ -4791,12 +4791,14 @@ pickvampshape(struct monst *mon)
         if (mon_has_special(mon))
             break; /* leave mndx as is */
         wolfchance = 3;
+        FALLTHROUGH;
     /*FALLTHRU*/
     case PM_VAMPIRE_LEADER: /* vampire lord or Vlad can become wolf */
         if (!rn2(wolfchance) && !uppercase_only) {
             mndx = PM_WOLF;
             break;
         }
+        FALLTHROUGH;
     /*FALLTHRU*/
     case PM_VAMPIRE: /* any vampire can become fog or bat */
         mndx = (!rn2(4) && !uppercase_only) ? PM_FOG_CLOUD : PM_VAMPIRE_BAT;
@@ -4900,6 +4902,7 @@ validvamp(struct monst *mon, int *mndx_p, int monclass)
             *mndx_p = PM_WOLF;
             break;
         }
+        FALLTHROUGH;
         /*FALLTHRU*/
     default:
         *mndx_p = NON_PM;
diff --git a/src/monmove.c b/src/monmove.c
index 0b5cde2e1..f27f8bdee 100644
--- a/src/monmove.c
+++ b/src/monmove.c
@@ -887,6 +887,7 @@ dochug(struct monst *mtmp)
         case MMOVE_NOMOVES:
             if (scared)
                 panicattk = TRUE;
+            FALLTHROUGH;
             /*FALLTHRU*/
         case MMOVE_NOTHING: /* no movement, but it can still attack you */
         case MMOVE_DONE: /* absolutely no movement */
@@ -1758,6 +1759,7 @@ m_move(struct monst *mtmp, int after)
             break;
         default:
             impossible("unknown shk/gd/pri_move return value (%d)", xm);
+            FALLTHROUGH;
             /*FALLTHRU*/
         case 0:
         case 1:
diff --git a/src/mthrowu.c b/src/mthrowu.c
index 455220098..5c41ea428 100644
--- a/src/mthrowu.c
+++ b/src/mthrowu.c
@@ -655,6 +655,7 @@ m_throw(
                     hitu = 0;
                     break;
                 }
+                FALLTHROUGH;
                 /*FALLTHRU*/
             case CREAM_PIE:
             case BLINDING_VENOM:
@@ -851,6 +852,7 @@ spitmm(struct monst *mtmp, struct attack *mattk, struct monst *mtarg)
             break;
         default:
             impossible("bad attack type in spitmm");
+            FALLTHROUGH;
             /*FALLTHRU*/
         case AD_ACID:
             otmp = mksobj(ACID_VENOM, TRUE, FALSE);
diff --git a/src/muse.c b/src/muse.c
index cb2c72a2b..0cece8f6a 100644
--- a/src/muse.c
+++ b/src/muse.c
@@ -1201,6 +1201,7 @@ rnd_defensive_item(struct monst *mtmp)
             goto try_again;
         if (!rn2(3))
             return WAN_TELEPORTATION;
+        FALLTHROUGH;
         /*FALLTHRU*/
     case 0:
     case 1:
@@ -1209,6 +1210,7 @@ rnd_defensive_item(struct monst *mtmp)
     case 10:
         if (!rn2(3))
             return WAN_CREATE_MONSTER;
+        FALLTHROUGH;
         /*FALLTHRU*/
     case 2:
         return SCR_CREATE_MONSTER;
@@ -1968,7 +1970,9 @@ rnd_offensive_item(struct monst *mtmp)
         if (hard_helmet(mtmp_helmet) || amorphous(pm)
             || passes_walls(pm) || noncorporeal(pm) || unsolid(pm))
             return SCR_EARTH;
-    } /* fall through */
+    }
+    FALLTHROUGH;
+    /* FALLTHRU */
     case 1:
         return WAN_STRIKING;
     case 2:
diff --git a/src/music.c b/src/music.c
index 241f53aee..82fe8abcc 100644
--- a/src/music.c
+++ b/src/music.c
@@ -443,6 +443,7 @@ do_earthquake(int force)
                 unblock_point(x, y);
                 if (cansee(x, y))
                     pline("A secret corridor is revealed.");
+                FALLTHROUGH;
                 /*FALLTHRU*/
             case CORR:
             case ROOM:
@@ -452,6 +453,7 @@ do_earthquake(int force)
                 cvt_sdoor_to_door(&levl[x][y]); /* .typ = DOOR */
                 if (cansee(x, y))
                     pline("A secret door is revealed.");
+                FALLTHROUGH;
                 /*FALLTHRU*/
             case DOOR: /* make the door collapse */
                 /* if already doorless, treat like room or corridor */
diff --git a/src/nhlua.c b/src/nhlua.c
index 08de9cfe1..becef1302 100644
--- a/src/nhlua.c
+++ b/src/nhlua.c
@@ -1996,6 +1996,8 @@ nhl_pcall_handle(lua_State *L, int nargs, int nresults, const char *name,
         case NHLpa_panic:
             panic("Lua error %d:%s %s", nud->sid,
                   nud->name ? nud->name : "(unknown)", lua_tostring(L, -1));
+            /*NOTREACHED*/
+            break;
         case NHLpa_impossible:
             impossible("Lua error: %d:%s %s", nud->sid,
                        nud->name ? nud->name : "(unknown)",
diff --git a/src/objnam.c b/src/objnam.c
index 334d5b7ed..94315442a 100644
--- a/src/objnam.c
+++ b/src/objnam.c
@@ -677,6 +677,7 @@ xname_flags(
     case WEAPON_CLASS:
         if (is_poisonable(obj) && obj->opoisoned)
             Strcpy(buf, "poisoned ");
+        FALLTHROUGH;
         /*FALLTHRU*/
     case VENOM_CLASS:
     case TOOL_CLASS:
@@ -1391,6 +1392,7 @@ doname_base(
                     ConcatF1(bp, 1, ", %s lit)", arti_light_description(obj));
             }
         }
+        FALLTHROUGH;
         /*FALLTHRU*/
     case WEAPON_CLASS:
         if (ispoisoned)
@@ -5077,7 +5079,8 @@ readobjnam(char *bp, struct obj *no_wish)
         break;
     case SLIME_MOLD:
         d.otmp->spe = d.ftype;
-    /* Fall through */
+        FALLTHROUGH;
+    /* FALLTHRU */
     case SKELETON_KEY:
     case CHEST:
     case LARGE_BOX:
@@ -5109,7 +5112,8 @@ readobjnam(char *bp, struct obj *no_wish)
     /* scroll of mail:  0: delivered in-game via external event (or randomly
        for fake mail); 1: from bones or wishing; 2: written with marker */
     case SCR_MAIL:
-        /*FALLTHRU*/
+        d.otmp->spe = 1;
+	break;
 #endif
     /* splash of venom:  0: normal, and transitory; 1: wishing */
     case ACID_VENOM:
@@ -5121,6 +5125,7 @@ readobjnam(char *bp, struct obj *no_wish)
             d.otmp->spe = (rn2(10) ? -1 : 0);
             break;
         }
+        FALLTHROUGH;
         /*FALLTHRU*/
     default:
         d.otmp->spe = d.spe;
diff --git a/src/options.c b/src/options.c
index 8abfcdc59..0a9a7dc85 100644
--- a/src/options.c
+++ b/src/options.c
@@ -3624,6 +3624,7 @@ optfn_scores(
                                      allopt[optidx].name);
                     return optn_silenterr;
                 }
+                FALLTHROUGH;
                 /*FALLTHRU*/
             default:
                 config_error_add("Unknown %s parameter '%s'",
diff --git a/src/pager.c b/src/pager.c
index 079d182a7..d067b3f87 100644
--- a/src/pager.c
+++ b/src/pager.c
@@ -765,6 +765,7 @@ lookat(coordxy x, coordxy y, char *buf, char *monbuf)
                 Strcpy(buf, "stone");
                 break;
             }
+            FALLTHROUGH;
             /*FALLTHRU*/
         default:
             Strcpy(buf, defsyms[symidx].explanation);
diff --git a/src/pickup.c b/src/pickup.c
index df8896fe4..a1c2ccb78 100644
--- a/src/pickup.c
+++ b/src/pickup.c
@@ -870,6 +870,7 @@ pickup(int what) /* should be a long */
                     lcount = (long) yn_number;
                     if (lcount > obj->quan)
                         lcount = obj->quan;
+                    FALLTHROUGH;
                     /*FALLTHRU*/
                 default: /* 'y' */
                     break;
@@ -1478,6 +1479,7 @@ query_category(
                         /* assert( n == 1 ); */
                         break; /* from switch */
                     }
+                    FALLTHROUGH;
                     /*FALLTHRU*/
                 case 'q':
                 default:
diff --git a/src/polyself.c b/src/polyself.c
index 9d619f6bb..38f9b01ea 100644
--- a/src/polyself.c
+++ b/src/polyself.c
@@ -1450,6 +1450,7 @@ dospit(void)
             break;
         default:
             impossible("bad attack type in dospit");
+            FALLTHROUGH;
             /*FALLTHRU*/
         case AD_ACID:
             otmp = mksobj(ACID_VENOM, TRUE, FALSE);
diff --git a/src/potion.c b/src/potion.c
index 68c9d165e..25989fff5 100644
--- a/src/potion.c
+++ b/src/potion.c
@@ -1721,16 +1721,19 @@ potionhit(struct monst *mon, struct obj *obj, int how)
         switch (obj->otyp) {
         case POT_FULL_HEALING:
             cureblind = TRUE;
+            FALLTHROUGH;
             /*FALLTHRU*/
         case POT_EXTRA_HEALING:
             if (!obj->cursed)
                 cureblind = TRUE;
+            FALLTHROUGH;
             /*FALLTHRU*/
         case POT_HEALING:
             if (obj->blessed)
                 cureblind = TRUE;
             if (mon->data == &mons[PM_PESTILENCE])
                 goto do_illness;
+            FALLTHROUGH;
             /*FALLTHRU*/
         case POT_RESTORE_ABILITY:
         case POT_GAIN_ABILITY:
@@ -1960,6 +1963,7 @@ potionbreathe(struct obj *obj)
         if (u.uhp < u.uhpmax)
             u.uhp++, disp.botl = TRUE;
         cureblind = TRUE;
+        FALLTHROUGH;
         /*FALLTHRU*/
     case POT_EXTRA_HEALING:
         if (Upolyd && u.mh < u.mhmax)
@@ -1968,6 +1972,7 @@ potionbreathe(struct obj *obj)
             u.uhp++, disp.botl = TRUE;
         if (!obj->cursed)
             cureblind = TRUE;
+        FALLTHROUGH;
         /*FALLTHRU*/
     case POT_HEALING:
         if (Upolyd && u.mh < u.mhmax)
@@ -2116,6 +2121,7 @@ mixtype(struct obj *o1, struct obj *o2)
     case POT_HEALING:
         if (o2typ == POT_SPEED)
             return POT_EXTRA_HEALING;
+        FALLTHROUGH;
         /*FALLTHRU*/
     case POT_EXTRA_HEALING:
     case POT_FULL_HEALING:
@@ -2123,6 +2129,7 @@ mixtype(struct obj *o1, struct obj *o2)
             return (o1typ == POT_HEALING) ? POT_EXTRA_HEALING
                    : (o1typ == POT_EXTRA_HEALING) ? POT_FULL_HEALING
                      : POT_GAIN_ABILITY;
+        FALLTHROUGH;
         /*FALLTHRU*/
     case UNICORN_HORN:
         switch (o2typ) {
diff --git a/src/pray.c b/src/pray.c
index 360030e65..b77c4faae 100644
--- a/src/pray.c
+++ b/src/pray.c
@@ -403,7 +403,8 @@ fix_worst_trouble(int trouble)
         break;
     case TROUBLE_STARVING:
         /* temporarily lost strength recovery now handled by init_uhunger() */
-        /*FALLTHRU*/
+        FALLTHROUGH;
+	/* FALLTHRU*/
     case TROUBLE_HUNGRY:
         Your("%s feels content.", body_part(STOMACH));
         init_uhunger();
@@ -745,7 +746,9 @@ angrygods(aligntyp resp_god)
             gods_angry(resp_god);
             punish((struct obj *) 0);
             break;
-        } /* else fall thru */
+        }
+	FALLTHROUGH;
+	/* FALLTHRU */
     case 4:
     case 5:
         gods_angry(resp_god);
@@ -1127,6 +1130,7 @@ pleased(aligntyp g_align)
         switch (min(action, 5)) {
         case 5:
             pat_on_head = 1;
+            FALLTHROUGH;
             /*FALLTHRU*/
         case 4:
             do
@@ -1137,8 +1141,9 @@ pleased(aligntyp g_align)
         case 3:
             /* up to 10 troubles */
             fix_worst_trouble(trouble);
+            FALLTHROUGH;
             /*FALLTHRU*/
-        case 2:
+	    case 2:
             /* up to 9 troubles */
             while ((trouble = in_trouble()) > 0 && (++tryct < 10))
                 fix_worst_trouble(trouble);
@@ -1234,6 +1239,7 @@ pleased(aligntyp g_align)
                     break;
                 }
             }
+            FALLTHROUGH;
             /*FALLTHRU*/
         case 2:
             if (!Blind)
@@ -1335,6 +1341,7 @@ pleased(aligntyp g_align)
                 gcrownu();
                 break;
             }
+            FALLTHROUGH;
             /*FALLTHRU*/
         case 6:
             give_spell();
@@ -2335,18 +2342,23 @@ maybe_turn_mon_iter(struct monst *mtmp)
                    than zombies. */
             case S_LICH:
                 xlev += 2;
+                FALLTHROUGH;
                 /*FALLTHRU*/
             case S_GHOST:
                 xlev += 2;
+                FALLTHROUGH;
                 /*FALLTHRU*/
             case S_VAMPIRE:
                 xlev += 2;
+                FALLTHROUGH;
                 /*FALLTHRU*/
             case S_WRAITH:
                 xlev += 2;
+                FALLTHROUGH;
                 /*FALLTHRU*/
             case S_MUMMY:
                 xlev += 2;
+                FALLTHROUGH;
                 /*FALLTHRU*/
             case S_ZOMBIE:
                 if (u.ulevel >= xlev && !resist(mtmp, '\0', 0, NOTELL)) {
@@ -2358,6 +2370,7 @@ maybe_turn_mon_iter(struct monst *mtmp)
                     }
                     break;
                 } /* else flee */
+                FALLTHROUGH;
                 /*FALLTHRU*/
             default:
                 monflee(mtmp, 0, FALSE, TRUE);
@@ -2656,6 +2669,7 @@ blocked_boulder(int dx, int dy)
         /* this is only approximate since multiple boulders might sink */
         if (is_pool_or_lava(nx, ny)) /* does its own isok() check */
             break; /* still need Sokoban check below */
+        FALLTHROUGH;
         /*FALLTHRU*/
     default:
         /* more than one boulder--blocked after they push the top one;
diff --git a/src/questpgr.c b/src/questpgr.c
index 29ef494c8..9f630e05a 100644
--- a/src/questpgr.c
+++ b/src/questpgr.c
@@ -374,6 +374,7 @@ convert_line(char *in_line, char *out_line)
                 /* pluralize */
                 case 'P':
                     gc.cvt_buf[0] = highc(gc.cvt_buf[0]);
+                    FALLTHROUGH;
                     /*FALLTHRU*/
                 case 'p':
                     Strcpy(gc.cvt_buf, makeplural(gc.cvt_buf));
@@ -382,6 +383,7 @@ convert_line(char *in_line, char *out_line)
                 /* append possessive suffix */
                 case 'S':
                     gc.cvt_buf[0] = highc(gc.cvt_buf[0]);
+                    FALLTHROUGH;
                     /*FALLTHRU*/
                 case 's':
                     Strcpy(gc.cvt_buf, s_suffix(gc.cvt_buf));
@@ -403,8 +405,9 @@ convert_line(char *in_line, char *out_line)
                 Strcat(cc, gc.cvt_buf);
                 cc += strlen(gc.cvt_buf);
                 break;
-            } /* else fall through */
-
+            }
+	    FALLTHROUGH;
+	    /* FALLTHRU */
         default:
             *cc++ = *c;
             break;
diff --git a/src/role.c b/src/role.c
index 7055ff5b7..3d036f1cb 100644
--- a/src/role.c
+++ b/src/role.c
@@ -1357,6 +1357,7 @@ clearrolefilter(int which)
     switch (which) {
     case RS_filter:
         gr.rfilter.mask = 0; /* clear race, gender, and alignment filters */
+        FALLTHROUGH;
         /*FALLTHRU*/
     case RS_ROLE:
         for (i = 0; i < SIZE(roles) - 1; ++i)
diff --git a/src/rumors.c b/src/rumors.c
index 11545fb6d..31fb19a82 100644
--- a/src/rumors.c
+++ b/src/rumors.c
@@ -563,6 +563,7 @@ outrumor(
         return;
     case BY_COOKIE:
         pline(fortune_msg);
+        FALLTHROUGH;
     /* FALLTHRU */
     case BY_PAPER:
         pline("It reads:");
diff --git a/src/selvar.c b/src/selvar.c
index 1951edfb8..5d08ca95e 100644
--- a/src/selvar.c
+++ b/src/selvar.c
@@ -582,6 +582,7 @@ selection_do_gradient(
     switch (gtyp) {
     default:
         impossible("Unrecognized gradient type! Defaulting to radial...");
+        FALLTHROUGH;
         /* FALLTHRU */
     case SEL_GRADIENT_RADIAL: {
         for (dx = 0; dx < COLNO; dx++)
diff --git a/src/shk.c b/src/shk.c
index 0ec28f217..d9077322f 100644
--- a/src/shk.c
+++ b/src/shk.c
@@ -4068,6 +4068,7 @@ sellobj(
         switch (gs.sell_response ? gs.sell_response : nyaq(qbuf)) {
         case 'q':
             gs.sell_response = 'n';
+            FALLTHROUGH;
             /*FALLTHRU*/
         case 'n':
             if (container)
@@ -4078,6 +4079,7 @@ sellobj(
             break;
         case 'a':
             gs.sell_response = 'y';
+            FALLTHROUGH;
             /*FALLTHRU*/
         case 'y':
             if (container)
diff --git a/src/sit.c b/src/sit.c
index 82fccb6e9..1f919d922 100644
--- a/src/sit.c
+++ b/src/sit.c
@@ -158,6 +158,7 @@ throne_sit_effect(void)
                     default:
                     case 2: /* more than 1 eye */
                         eye = makeplural(eye);
+                        FALLTHROUGH;
                         /*FALLTHRU*/
                     case 1: /* one eye (Cyclops, floating eye) */
                         Your("%s %s...", eye, vtense(eye, "tingle"));
@@ -517,6 +518,7 @@ attrcurse(void)
             ret = FIRE_RES;
             break;
         }
+        FALLTHROUGH;
         /*FALLTHRU*/
     case 2:
         if (HTeleportation & INTRINSIC) {
@@ -525,6 +527,7 @@ attrcurse(void)
             ret = TELEPORT;
             break;
         }
+        FALLTHROUGH;
         /*FALLTHRU*/
     case 3:
         if (HPoison_resistance & INTRINSIC) {
@@ -533,6 +536,7 @@ attrcurse(void)
             ret = POISON_RES;
             break;
         }
+        FALLTHROUGH;
         /*FALLTHRU*/
     case 4:
         if (HTelepat & INTRINSIC) {
@@ -543,6 +547,7 @@ attrcurse(void)
             ret = TELEPAT;
             break;
         }
+        FALLTHROUGH;
         /*FALLTHRU*/
     case 5:
         if (HCold_resistance & INTRINSIC) {
@@ -551,6 +556,7 @@ attrcurse(void)
             ret = COLD_RES;
             break;
         }
+        FALLTHROUGH;
         /*FALLTHRU*/
     case 6:
         if (HInvis & INTRINSIC) {
@@ -559,6 +565,7 @@ attrcurse(void)
             ret = INVIS;
             break;
         }
+        FALLTHROUGH;
         /*FALLTHRU*/
     case 7:
         if (HSee_invisible & INTRINSIC) {
@@ -574,6 +581,7 @@ attrcurse(void)
             ret = SEE_INVIS;
             break;
         }
+        FALLTHROUGH;
         /*FALLTHRU*/
     case 8:
         if (HFast & INTRINSIC) {
@@ -582,6 +590,7 @@ attrcurse(void)
             ret = FAST;
             break;
         }
+        FALLTHROUGH;
         /*FALLTHRU*/
     case 9:
         if (HStealth & INTRINSIC) {
@@ -590,6 +599,7 @@ attrcurse(void)
             ret = STEALTH;
             break;
         }
+        FALLTHROUGH;
         /*FALLTHRU*/
     case 10:
         /* intrinsic protection is just disabled, not set back to 0 */
@@ -599,6 +609,7 @@ attrcurse(void)
             ret = PROTECTION;
             break;
         }
+        FALLTHROUGH;
         /*FALLTHRU*/
     case 11:
         if (HAggravate_monster & INTRINSIC) {
@@ -607,6 +618,7 @@ attrcurse(void)
             ret = AGGRAVATE_MONSTER;
             break;
         }
+        FALLTHROUGH;
         /*FALLTHRU*/
     default:
         break;
diff --git a/src/sounds.c b/src/sounds.c
index eac50772a..5a5e9fd66 100644
--- a/src/sounds.c
+++ b/src/sounds.c
@@ -264,6 +264,7 @@ dosounds(void)
                     break;
                 }
             }
+            FALLTHROUGH;
                 /*FALLTHRU*/
             case 0:
                 Soundeffect(se_guards_footsteps, 30);
@@ -631,7 +632,6 @@ cry_sound(struct monst *mtmp)
         ret = "hiss";
         break;
     case MS_ROAR: /* baby dragons; have them growl instead of roar */
-        /*FALLTHRU*/
     case MS_GROWL: /* (none) */
         ret = "growl";
         break;
@@ -870,6 +870,7 @@ domonnoise(struct monst *mtmp)
             }
             break;
         }
+        FALLTHROUGH;
         /*FALLTHRU*/
     case MS_GROWL:
         Soundeffect((mtmp->mpeaceful ? se_snarl : se_growl), 80);
@@ -1019,6 +1020,7 @@ domonnoise(struct monst *mtmp)
             }
             break;
         }
+        FALLTHROUGH;
         /*FALLTHRU*/
     case MS_HUMANOID:
         if (!mtmp->mpeaceful) {
@@ -1141,7 +1143,8 @@ domonnoise(struct monst *mtmp)
             (void) demon_talk(mtmp);
             break;
         }
-    /* fall through */
+	FALLTHROUGH;
+        /* FALLTHRU */
     case MS_CUSS:
         if (!mtmp->mpeaceful)
             cuss(mtmp);
diff --git a/src/spell.c b/src/spell.c
index 65ef028b1..3ef28cafa 100644
--- a/src/spell.c
+++ b/src/spell.c
@@ -1441,11 +1441,13 @@ spelleffects(int spell_otyp, boolean atme, boolean force)
             }
             break;
         } /* else */
+        FALLTHROUGH;
         /*FALLTHRU*/
 
     /* these spells are all duplicates of wand effects */
     case SPE_FORCE_BOLT:
         physical_damage = TRUE;
+        FALLTHROUGH;
     /*FALLTHRU*/
     case SPE_SLEEP:
     case SPE_MAGIC_MISSILE:
@@ -1510,6 +1512,7 @@ spelleffects(int spell_otyp, boolean atme, boolean force)
         /* high skill yields effect equivalent to blessed scroll */
         if (role_skill >= P_SKILLED)
             pseudo->blessed = 1;
+        FALLTHROUGH;
     /*FALLTHRU*/
     case SPE_CHARM_MONSTER:
     case SPE_MAGIC_MAPPING:
@@ -1526,6 +1529,7 @@ spelleffects(int spell_otyp, boolean atme, boolean force)
         /* high skill yields effect equivalent to blessed potion */
         if (role_skill >= P_SKILLED)
             pseudo->blessed = 1;
+        FALLTHROUGH;
     /*FALLTHRU*/
     case SPE_INVISIBILITY:
         (void) peffects(pseudo);
diff --git a/src/steed.c b/src/steed.c
index 2c7be9c2e..84a6e9287 100644
--- a/src/steed.c
+++ b/src/steed.c
@@ -589,6 +589,7 @@ dismount_steed(
     switch (reason) {
     case DISMOUNT_THROWN:
         verb = "are thrown";
+        FALLTHROUGH;
         /*FALLTHRU*/
     case DISMOUNT_KNOCKED:
     case DISMOUNT_FELL:
diff --git a/src/timeout.c b/src/timeout.c
index cb9800994..4ec9f9c6b 100644
--- a/src/timeout.c
+++ b/src/timeout.c
@@ -214,6 +214,7 @@ vomiting_dialogue(void)
         make_stunned((HStun & TIMEOUT) + (long) d(2, 4), FALSE);
         if (!Popeye(VOMITING))
             stop_occupation();
+        FALLTHROUGH;
     /*FALLTHRU*/
     case 9:
         make_confused((HConfusion & TIMEOUT) + (long) d(2, 4), FALSE);
@@ -1441,6 +1442,7 @@ burn_object(anything *arg, long timeout)
             switch (obj->where) {
             case OBJ_INVENT:
                 need_invupdate = TRUE;
+                FALLTHROUGH;
                 /*FALLTHRU*/
             case OBJ_MINVENT:
                 pline("%spotion of oil has burnt away.", whose);
@@ -1504,6 +1506,7 @@ burn_object(anything *arg, long timeout)
                 switch (obj->where) {
                 case OBJ_INVENT:
                     need_invupdate = TRUE;
+                    FALLTHROUGH;
                     /*FALLTHRU*/
                 case OBJ_MINVENT:
                     if (obj->otyp == BRASS_LANTERN)
@@ -1583,6 +1586,7 @@ burn_object(anything *arg, long timeout)
                     switch (obj->where) {
                     case OBJ_INVENT:
                         need_invupdate = TRUE;
+                        FALLTHROUGH;
                         /*FALLTHRU*/
                     case OBJ_MINVENT:
                         pline("%scandelabrum's flame%s.", whose,
@@ -1598,6 +1602,7 @@ burn_object(anything *arg, long timeout)
                     case OBJ_INVENT:
                         /* no need_invupdate for update_inventory() necessary;
                            useupall() -> freeinv() handles it */
+                           FALLTHROUGH;
                         /*FALLTHRU*/
                     case OBJ_MINVENT:
                         pline("%s %s consumed!", Yname2(obj),
diff --git a/src/topten.c b/src/topten.c
index f38de9244..cb968a726 100644
--- a/src/topten.c
+++ b/src/topten.c
@@ -110,11 +110,13 @@ formatkiller(
     switch (svk.killer.format) {
     default:
         impossible("bad killer format? (%d)", svk.killer.format);
+        FALLTHROUGH;
         /*FALLTHRU*/
     case NO_KILLER_PREFIX:
         break;
     case KILLED_BY_AN:
         kname = an(kname);
+        FALLTHROUGH;
         /*FALLTHRU*/
     case KILLED_BY:
         (void) strncat(buf, killed_by_prefix[how], siz - 1);
diff --git a/src/trap.c b/src/trap.c
index a39ba8ddc..da39e4428 100644
--- a/src/trap.c
+++ b/src/trap.c
@@ -513,6 +513,7 @@ maketrap(coordxy x, coordxy y, int typ)
     case PIT:
     case SPIKED_PIT:
         ttmp->conjoined = 0;
+        FALLTHROUGH;
         /*FALLTHRU*/
     case HOLE:
     case TRAPDOOR:
@@ -1126,10 +1127,13 @@ m_harmless_trap(struct monst *mtmp, struct trap *ttmp)
             return TRUE;
         break;
     case PIT:
+        FALLTHROUGH;
         /*FALLTHRU*/
     case SPIKED_PIT:
+        FALLTHROUGH;
         /*FALLTHRU*/
     case HOLE:
+        FALLTHROUGH;
         /*FALLTHRU*/
     case TRAPDOOR:
         if (is_clinger(mdat) && !Sokoban)
@@ -2190,6 +2194,7 @@ trapeffect_web(
                 mtmp->mtrapped = 1;
                 break;
             }
+            FALLTHROUGH;
             /*FALLTHRU*/
         default:
             if (mptr->mlet == S_GIANT
@@ -2721,6 +2726,7 @@ immune_to_trap(struct monst *mon, unsigned ttype)
         if (pm->msize <= MZ_SMALL
             || amorphous(pm) || is_whirly(pm) || unsolid(pm))
             return TRAP_CLEARLY_IMMUNE;
+        FALLTHROUGH;
         /*FALLTHRU*/
     case SQKY_BOARD:
     case LANDMINE:
@@ -2809,6 +2815,7 @@ immune_to_trap(struct monst *mon, unsigned ttype)
            for monsters, only replicates fire trap, so fall through */
         if (is_you)
             return TRAP_NOT_IMMUNE;
+        FALLTHROUGH;
         /*FALLTHRU*/
     case FIRE_TRAP: /* can always destroy items being carried */
         /* harmful if not resistant or if carrying anything that could burn */
@@ -3244,10 +3251,12 @@ launch_obj(
         /* use otrapped as a flag to ohitmon */
         singleobj->otrapped = 1;
         style &= ~LAUNCH_KNOWN;
+        FALLTHROUGH;
     /*FALLTHRU*/
     case ROLL:
  roll:
         delaycnt = 2;
+        FALLTHROUGH;
     /*FALLTHRU*/
     default:
         if (!delaycnt)
@@ -3352,6 +3361,7 @@ launch_obj(
                     /* if trap doesn't work, skip "disappears" message */
                     if (newlev == depth(&u.uz))
                         break;
+                    FALLTHROUGH;
                     /*FALLTHRU*/
                 case TELEP_TRAP:
                     if (cansee(x, y))
@@ -4050,6 +4060,7 @@ float_down(
         case TRAPDOOR:
             if (!Can_fall_thru(&u.uz) || u.ustuck)
                 break;
+            FALLTHROUGH;
             /*FALLTHRU*/
         default:
             if (!u.utrap) /* not already in the trap */
diff --git a/src/uhitm.c b/src/uhitm.c
index da34794a9..9aaa11332 100644
--- a/src/uhitm.c
+++ b/src/uhitm.c
@@ -3772,6 +3772,7 @@ mhitm_ad_deth(
                 mhm->damage = 0;
                 return;
             }
+            FALLTHROUGH;
             /*FALLTHRU*/
         default: /* case 16: ... case 5: */
             You_feel("your life force draining away...");
@@ -5385,10 +5386,12 @@ hmonas(struct monst *mon)
         case AT_CLAW:
             if (uwep && !cantwield(gy.youmonst.data) && !weapon_used)
                 goto use_weapon;
+            FALLTHROUGH;
             /*FALLTHRU*/
         case AT_TUCH:
             if (uwep && gy.youmonst.data->mlet == S_LICH && !weapon_used)
                 goto use_weapon;
+            FALLTHROUGH;
             /*FALLTHRU*/
         case AT_KICK:
         case AT_BITE:
@@ -5632,6 +5635,7 @@ hmonas(struct monst *mon)
                  || gy.youmonst.data->mlet == S_ORC
                  || gy.youmonst.data->mlet == S_GNOME) && !weapon_used)
                 goto use_weapon;
+            FALLTHROUGH;
             /*FALLTHRU*/
 
         case AT_NONE:
@@ -6016,6 +6020,8 @@ passive_obj(
             }
             break;
         }
+	FALLTHROUGH;
+	/* FALLTHRU */
     default:
         break;
     }
diff --git a/src/weapon.c b/src/weapon.c
index d65c64945..5234c2781 100644
--- a/src/weapon.c
+++ b/src/weapon.c
@@ -1466,7 +1466,9 @@ weapon_hit_bonus(struct obj *weapon)
     } else if (type <= P_LAST_WEAPON) {
         switch (P_SKILL(type)) {
         default:
-            impossible(bad_skill, P_SKILL(type)); /* fall through */
+            impossible(bad_skill, P_SKILL(type));
+            FALLTHROUGH;
+            /* FALLTHRU */
         case P_ISRESTRICTED:
         case P_UNSKILLED:
             bonus = -4;
@@ -1487,7 +1489,9 @@ weapon_hit_bonus(struct obj *weapon)
             skill = P_SKILL(wep_type);
         switch (skill) {
         default:
-            impossible(bad_skill, skill); /* fall through */
+            impossible(bad_skill, skill);
+            FALLTHROUGH;
+            /* FALLTHRU */
         case P_ISRESTRICTED:
         case P_UNSKILLED:
             bonus = -9;
@@ -1561,7 +1565,8 @@ weapon_dam_bonus(struct obj *weapon)
         switch (P_SKILL(type)) {
         default:
             impossible("weapon_dam_bonus: bad skill %d", P_SKILL(type));
-        /* fall through */
+            FALLTHROUGH;
+        /* FALLTHRU */
         case P_ISRESTRICTED:
         case P_UNSKILLED:
             bonus = -2;
diff --git a/src/wizard.c b/src/wizard.c
index aefba556d..8db22f060 100644
--- a/src/wizard.c
+++ b/src/wizard.c
@@ -284,8 +284,8 @@ strategy(struct monst *mtmp)
     case 1: /* the wiz is less cautious */
         if (mtmp->data != &mons[PM_WIZARD_OF_YENDOR])
             return (unsigned long) STRAT_HEAL;
-    /* else fall through */
-
+        FALLTHROUGH;
+	/* FALLTHRU */
     case 2:
         dstrat = STRAT_HEAL;
         break;
@@ -399,6 +399,7 @@ tactics(struct monst *mtmp)
                 mtmp->mhp += rnd(8);
                 return 1;
             }
+        FALLTHROUGH;
         /*FALLTHRU*/
 
     case STRAT_NONE: /* harass */
diff --git a/src/wizcmds.c b/src/wizcmds.c
index 12f51758c..c7cdd707e 100644
--- a/src/wizcmds.c
+++ b/src/wizcmds.c
@@ -1065,6 +1065,7 @@ wiz_intrinsic(void)
                    so needs more than simple incr_itimeout() but we want
                    the pline() issued with that */
                 make_glib((int) newtimeout);
+                FALLTHROUGH;
                 /*FALLTHRU*/
             default:
  def_feedback:
diff --git a/src/zap.c b/src/zap.c
index dede87a0d..59c871edc 100644
--- a/src/zap.c
+++ b/src/zap.c
@@ -177,6 +177,7 @@ bhitm(struct monst *mtmp, struct obj *otmp)
     switch (otyp) {
     case WAN_STRIKING:
         zap_type_text = "wand";
+        FALLTHROUGH;
     /*FALLTHRU*/
     case SPE_FORCE_BOLT:
         reveal_invis = TRUE;
@@ -1096,6 +1097,7 @@ revive(struct obj *corpse, boolean by_hero)
             obfree(corpse, (struct obj *) 0);
             break;
         }
+        FALLTHROUGH;
         /*FALLTHRU*/
     case OBJ_FREE:
     case OBJ_MIGRATING:
@@ -2056,6 +2058,7 @@ stone_to_flesh_obj(struct obj *obj) /* nonnull */
         smell = TRUE;
         break;
     case WEAPON_CLASS: /* crysknife */
+        FALLTHROUGH;
         /*FALLTHRU*/
     default:
         res = 0;
@@ -2869,6 +2872,7 @@ zapyourself(struct obj *obj, boolean ordinary)
     case WAN_LIGHT: /* (broken wand) */
         /* assert( !ordinary ); */
         damage = d(obj->spe, 25);
+        FALLTHROUGH;
         /*FALLTHRU*/
     case EXPENSIVE_CAMERA:
         if (!damage)
@@ -3243,6 +3247,7 @@ zap_updown(struct obj *obj) /* wand or spell, nonnull */
     case WAN_STRIKING:
     case SPE_FORCE_BOLT:
         striking = TRUE;
+        FALLTHROUGH;
         /*FALLTHRU*/
     case WAN_LOCKING:
     case SPE_WIZARD_LOCK:
@@ -4924,6 +4929,7 @@ dobuzz(
                 switch (bounce) {
                 case 0:
                     dx = -dx;
+                    FALLTHROUGH;
                     /*FALLTHRU*/
                 case 1:
                     dy = -dy;
@@ -5256,6 +5262,7 @@ zap_over_floor(
         break;
 
     case ZT_LIGHTNING:
+        FALLTHROUGH;
         /*FALLTHRU*/
     case ZT_ACID:
         if (lev->typ == IRONBARS) {
diff --git a/sys/msdos/video.c b/sys/msdos/video.c
index e172513ee..6397fa8d8 100644
--- a/sys/msdos/video.c
+++ b/sys/msdos/video.c
@@ -293,6 +293,7 @@ term_end_attr(int attr)
     switch (attr) {
     case ATR_INVERSE:
         inversed = 0;
+        FALLTHROUGH;
         /*FALLTHRU*/
     case ATR_ULINE:
     case ATR_BOLD:
@@ -341,6 +342,7 @@ term_start_attr(int attr)
         break;
     case ATR_INVERSE:
         inversed = 1;
+        FALLTHROUGH;
         /*FALLTHRU*/
     default:
         g_attribute = iflags.grmode ? attrib_gr_normal : attrib_text_normal;
diff --git a/sys/unix/hints/include/compiler.370 b/sys/unix/hints/include/compiler.370
index 3e95e151b..ae3dc8d19 100755
--- a/sys/unix/hints/include/compiler.370
+++ b/sys/unix/hints/include/compiler.370
@@ -78,20 +78,29 @@ CXX=g++ -std=gnu++11
 GCCGTEQ9 := $(shell expr `$(CC) -dumpversion | cut -f1 -d.` \>= 9)
 GCCGTEQ11 := $(shell expr `$(CC) -dumpversion | cut -f1 -d.` \>= 11)
 GCCGTEQ12 := $(shell expr `$(CC) -dumpversion | cut -f1 -d.` \>= 12)
+GCCGTEQ14 := $(shell expr `$(CC) -dumpversion | cut -f1 -d.` \>= 14)
 ifeq "$(GCCGTEQ9)" "1"
 # flags present in gcc version greater than or equal to 9 can go here
 CFLAGS+=-Wformat-overflow
 CFLAGS+=-Wmissing-parameter-type
 endif   # GCC greater than or equal to 9
 #ifeq "$(GCCGTEQ11)" "1"
+CFLAGS+=-Wimplicit-fallthrough
 #endif
 #ifeq "$(GCCGTEQ12)" "1"
 #endif
+#ifeq "$(GCCGTEQ14)" "1"
+CFLAGS+=-std=gnu23
+#endif
 # end of gcc-specific
 else   # gcc or clang?
 CXX=clang++ -std=gnu++11
 # clang-specific follows
+CLANGGTEQ12 := $(shell expr `$(CC) -dumpversion | cut -f1 -d.` \>= 12)
 CLANGGTEQ14 := $(shell expr `$(CC) -dumpversion | cut -f1 -d.` \>= 14)
+ifeq "$(CLANGGTEQ12)" "1"
+CFLAGS+=-Wimplicit-fallthrough
+endif
 ifeq "$(CLANGGTEQ14)" "1"
 ifneq "$(VIEWDEPRECATIONS)" "1"
 CFLAGS+=-Wno-deprecated-declarations
diff --git a/sys/unix/hints/include/cross-pre2.370 b/sys/unix/hints/include/cross-pre2.370
index fa5f0911c..8a7142985 100644
--- a/sys/unix/hints/include/cross-pre2.370
+++ b/sys/unix/hints/include/cross-pre2.370
@@ -142,6 +142,7 @@ MSDOS_TARGET_CFLAGS = -c -O -I../include -I../sys/msdos -I../win/share \
         -Wall -Wextra -Wno-missing-field-initializers -Wreturn-type -Wunused \
         -Wformat -Wswitch -Wshadow -Wwrite-strings \
 	-Wimplicit -Wimplicit-function-declaration -Wimplicit-int \
+	-Wimplicit-fallthrough \
 	-Wmissing-parameter-type -Wold-style-definition -Wstrict-prototypes
 MSDOS_TARGET_CXXFLAGS = -c -O -I../include -I../sys/msdos -I../win/share \
         $(LUAINCL) -DDLB $(PDCURSESDEF) \
diff --git a/sys/vms/vmsunix.c b/sys/vms/vmsunix.c
index f2c1bb0df..090ce9e64 100644
--- a/sys/vms/vmsunix.c
+++ b/sys/vms/vmsunix.c
@@ -241,6 +241,7 @@ vms_define(const char *name, const char *value, int flag)
     switch (flag) {
     case ENV_JOB: /* job logical name */
         tbl_dsc.len = strlen(tbl_dsc.adr = "LNM$JOB");
+        FALLTHROUGH;
     /*FALLTHRU*/
     case ENV_SUP: /* supervisor-mode process logical name */
         result = lib$set_logical(&nam_dsc, &val_dsc, &tbl_dsc);
diff --git a/sys/windows/Makefile.nmake b/sys/windows/Makefile.nmake
index 95b8bae17..07646b7f0 100644
--- a/sys/windows/Makefile.nmake
+++ b/sys/windows/Makefile.nmake
@@ -1131,10 +1131,18 @@ scall  =
 # 4777 format string requires an argument of type 'type',
 #      but variadic argument 'position' has type 'type'
 # 4820 padding in struct
+# 5262 enable fallthrough warnings that lack [[fallthrough]]
+#
 ctmpflags = $(ctmpflags:-W3=-W4) -wd4100 -wd4244 -wd4245 -wd4310 -wd4706 -w44777 -wd4820
 !IF ($(VSVER) >= 2019)
 ctmpflags = $(ctmpflags) -w44774
 !ENDIF
+!IF ($(VSVER) >= 2022)
+!IF ($(MAKEVERSION) >= 1440338120)
+# warning 5262 became available starting in Visual Studio 2022 version 17.4.
+ctmpflags = $(ctmpflags) -w45262 /std:clatest
+!ENDIF
+!ENDIF
 !ENDIF
 
 #More verbose warning output options below
@@ -2880,6 +2888,8 @@ $(OTTY)sfstruct.o: sfstruct.c $(HACK_H)
 $(OTTY)shk.o: shk.c $(HACK_H)
 $(OTTY)shknam.o: shknam.c $(HACK_H)
 $(OTTY)sit.o: sit.c $(HACK_H) $(INCL)\artifact.h
+	$(Q)$(CC) $(CFLAGS) /EP  $(@B).c > $(OTTY)$(@B).c.preproc
+	$(Q)$(CC) $(CFLAGS) -Fo$@ $(@B).c
 $(OTTY)sounds.o: sounds.c $(HACK_H)
 $(OTTY)sp_lev.o: sp_lev.c $(HACK_H) $(INCL)\sp_lev.h
 $(OTTY)spell.o: spell.c $(HACK_H)
diff --git a/sys/windows/consoletty.c b/sys/windows/consoletty.c
index 5f624bec8..30fe4cff7 100644
--- a/sys/windows/consoletty.c
+++ b/sys/windows/consoletty.c
@@ -1087,6 +1087,7 @@ CtrlHandler(DWORD ctrltype)
     /* case CTRL_C_EVENT: */
     case CTRL_BREAK_EVENT:
         term_clear_screen();
+        FALLTHROUGH;
     case CTRL_CLOSE_EVENT:
     case CTRL_LOGOFF_EVENT:
     case CTRL_SHUTDOWN_EVENT:
@@ -1335,7 +1336,8 @@ xputc_core(int ch)
     case '\n':
         if (console.cursor.Y < console.height - 1)
             console.cursor.Y++;
-    /* fall through */
+        FALLTHROUGH;
+    /* FALLTHRU */
     case '\r':
         console.cursor.X = 1;
         break;
@@ -1879,6 +1881,7 @@ toggle_mouse_support(void)
 #endif /* VIRTUAL_TERMINAL_SEQUENCES */
                 break;
         case 0:
+                FALLTHROUGH;
                 /*FALLTHRU*/
         default:
 #ifndef VIRTUAL_TERMINAL_SEQUENCES
diff --git a/sys/windows/windmain.c b/sys/windows/windmain.c
index 0cbded52d..df7e009b1 100644
--- a/sys/windows/windmain.c
+++ b/sys/windows/windmain.c
@@ -630,7 +630,7 @@ process_options(int argc, char * argv[])
                 break;
             } else
                 raw_printf("\nUnknown switch: %s", argv[0]);
-        /* FALL THROUGH */
+        FALLTHROUGH;
         case '?':
             nhusage();
             nethack_exit(EXIT_SUCCESS);
diff --git a/util/makedefs.c b/util/makedefs.c
index 6dfb582f2..cbb466848 100644
--- a/util/makedefs.c
+++ b/util/makedefs.c
@@ -846,7 +846,8 @@ do_grep_control(char *buf)
         break;
     case '!': /* if not ID */
         isif = 0;
-    /* FALLTHROUGH */
+        FALLTHROUGH;
+    /* FALLTHRU */
     case '?': /* if ID */
         if (grep_sp == GREP_STACK_SIZE - 2) {
             Fprintf(stderr, "stack overflow at line %d.", grep_lineno);
@@ -2302,6 +2303,7 @@ do_objs(void)
                 n_glass_gems++;
                 break;
             }
+            FALLTHROUGH;
             /*FALLTHRU*/
         case VENOM_CLASS:
             /* fall-through from gem class is ok; objects[] used to have
@@ -2311,6 +2313,7 @@ do_objs(void)
                so strip the extra "splash of " off to keep same macros */
             if (!strncmp(objnam, "SPLASH_OF_", 10))
                 objnam += 10;
+            FALLTHROUGH;
             /*FALLTHRU*/
         default:
             Fprintf(ofp, "#define\t");
diff --git a/win/Qt/qt_bind.cpp b/win/Qt/qt_bind.cpp
index d66377f3b..e6546447c 100644
--- a/win/Qt/qt_bind.cpp
+++ b/win/Qt/qt_bind.cpp
@@ -271,6 +271,7 @@ void NetHackQtBind::qt_askname()
             // success; handle plname[] verification below prior to returning
             break;
         }
+        FALLTHROUGH;
         /*FALLTHRU*/
     case -2:
         // Quit
@@ -726,6 +727,7 @@ char NetHackQtBind::qt_more()
             switch (ch) {
             case '\0': // hypothetical
                 ch = '\033';
+                FALLTHROUGH;
                 /*FALLTHRU*/
             case ' ':
             case '\n':
diff --git a/win/curses/cursdial.c b/win/curses/cursdial.c
index 5dbe9d796..a0e93d093 100644
--- a/win/curses/cursdial.c
+++ b/win/curses/cursdial.c
@@ -1556,6 +1556,7 @@ menu_get_selections(WINDOW *win, nhmenu *menu, int how)
                     break;
                 }
             }
+            FALLTHROUGH;
             /*FALLTHRU*/
         default:
             if (curletter > 0 && curletter < 256
diff --git a/win/curses/cursinit.c b/win/curses/cursinit.c
index de1811e7f..fcf13ec19 100644
--- a/win/curses/cursinit.c
+++ b/win/curses/cursinit.c
@@ -114,6 +114,7 @@ curses_create_main_windows(void)
 
     case 3:
         noperminv_borders = TRUE;
+        FALLTHROUGH;
         /*FALLTHRU*/
     case 1:                     /* On */
         borders = TRUE;
@@ -121,6 +122,7 @@ curses_create_main_windows(void)
 
     case 4:
         noperminv_borders = TRUE;
+        FALLTHROUGH;
         /*FALLTHRU*/
     case 2:                     /* Auto */
         borders = (term_cols >= 80 + 2 && term_rows >= 24 + 2);
diff --git a/win/curses/cursmisc.c b/win/curses/cursmisc.c
index 73a939f2a..71b9f31f6 100644
--- a/win/curses/cursmisc.c
+++ b/win/curses/cursmisc.c
@@ -291,7 +291,7 @@ curses_break_str(const char *str, int width, int line_num)
     char *retstr;
     int curline = 0;
     int strsize = (int) strlen(str) + 1;
-#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L
+#if (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L) && !defined(_MSC_VER)
     char substr[strsize];
     char curstr[strsize];
     char tmpstr[strsize];
@@ -363,7 +363,7 @@ curses_str_remainder(const char *str, int width, int line_num)
     char *retstr;
     int curline = 0;
     int strsize = strlen(str) + 1;
-#if __STDC_VERSION__ >= 199901L
+#if (__STDC_VERSION__ >= 199901L) && !defined(_MSC_VER)
     char substr[strsize];
     char tmpstr[strsize];
 
@@ -801,6 +801,7 @@ curses_convert_keys(int key)
            a value for ^H greater than 255 is passed back to core's
            readchar() and stripping the value down to 0..255 yields ^G! */
         ret = C('H');
+        FALLTHROUGH;
         /*FALLTHRU*/
     default:
         if (modifiers_available)
diff --git a/win/curses/cursstat.c b/win/curses/cursstat.c
index 15168f845..90a9d93c9 100644
--- a/win/curses/cursstat.c
+++ b/win/curses/cursstat.c
@@ -415,6 +415,7 @@ draw_horizontal(boolean border)
                         w -= (t - 30); /* '+= strlen()' below will add 't';
                                         * functional result being 'w += 30' */
                 }
+                FALLTHROUGH;
                 /*FALLTHRU*/
             case BL_ALIGN:
             case BL_LEVELDESC:
@@ -1231,6 +1232,7 @@ curs_vert_status_vals(int win_width)
                 if (fld_width < hp_width + 3) /* +3: " " gap and "("...")" */
                     Sprintf(leadingspace, "%*s",
                             (hp_width + 3) - fld_width, " ");
+                FALLTHROUGH;
                 /*FALLTHRU*/
             case BL_VERS:
             case BL_EXP:
diff --git a/win/curses/curswins.c b/win/curses/curswins.c
index fa99b58c4..19c6c380a 100644
--- a/win/curses/curswins.c
+++ b/win/curses/curswins.c
@@ -98,6 +98,7 @@ curses_create_window(int wid, int width, int height, orient orientation)
     switch (orientation) {
     default:
         impossible("curses_create_window: Bad orientation");
+        FALLTHROUGH;
         /*FALLTHRU*/
     case CENTER:
         startx = (term_cols / 2) - (width / 2);
diff --git a/win/tty/termcap.c b/win/tty/termcap.c
index 4cb40d4ea..2c6a5bd88 100644
--- a/win/tty/termcap.c
+++ b/win/tty/termcap.c
@@ -1341,6 +1341,7 @@ s_atr2str(int n)
         /* if italic isn't available, fall through to underline */
         if (ZH && *ZH)
             return ZH;
+        FALLTHROUGH;
         /*FALLTHRU*/
     case ATR_BLINK:
     case ATR_ULINE:
@@ -1351,6 +1352,7 @@ s_atr2str(int n)
             if (nh_US && *nh_US)
                 return nh_US;
         }
+        FALLTHROUGH;
         /*FALLTHRU*/
     case ATR_BOLD:
         if (MD && *MD)
@@ -1378,15 +1380,18 @@ e_atr2str(int n)
         /* send ZR unless we didn't have ZH and substituted US */
         if (ZR && *ZR && ZH && *ZH)
             return ZR;
+        FALLTHROUGH;
         /*FALLTHRU*/
     case ATR_ULINE:
         if (nh_UE && *nh_UE)
             return nh_UE;
+        FALLTHROUGH;
         /*FALLTHRU*/
     case ATR_BOLD:
     case ATR_BLINK:
         if (nh_HE && *nh_HE)
             return nh_HE;
+        FALLTHROUGH;
         /*FALLTHRU*/
     case ATR_DIM:
     case ATR_INVERSE:
diff --git a/win/tty/wintty.c b/win/tty/wintty.c
index 17dcd1cc2..693592fbb 100644
--- a/win/tty/wintty.c
+++ b/win/tty/wintty.c
@@ -665,6 +665,7 @@ tty_askname(void)
         case -1:
             bail("Until next time then..."); /* quit */
             /*NOTREACHED*/
+            break;
         case 0:
             break; /* no game chosen; start new game */
         case 1:
@@ -1084,6 +1085,7 @@ tty_clear_nhwindow(winid window)
     case NHW_MAP:
         /* cheap -- clear the whole thing and tell nethack to redraw botl */
         disp.botlx = TRUE;
+        FALLTHROUGH;
         /*FALLTHRU*/
     case NHW_BASE:
         /* if erasing_tty_screen is True, calling sequence is
@@ -1721,6 +1723,7 @@ process_menu_window(winid window, struct WinDesc *cw)
             break;
         case MENU_EXPLICIT_CHOICE:
             morc = really_morc;
+            FALLTHROUGH;
         /*FALLTHRU*/
         default:
             if (cw->how == PICK_NONE || !strchr(resp, morc)) {
@@ -1878,12 +1881,14 @@ tty_display_nhwindow(
             tty_display_nhwindow(WIN_MESSAGE, TRUE);
             return;
         }
+        FALLTHROUGH;
         /*FALLTHRU*/
     case NHW_BASE:
         (void) fflush(stdout);
         break;
     case NHW_TEXT:
         cw->maxcol = ttyDisplay->cols; /* force full-screen mode */
+        FALLTHROUGH;
         /*FALLTHRU*/
     case NHW_MENU:
         cw->active = 1;
@@ -1951,6 +1956,7 @@ tty_dismiss_nhwindow(winid window)
         if (ttyDisplay->toplin != TOPLINE_EMPTY)
             tty_display_nhwindow(WIN_MESSAGE, TRUE);
         nhassert(ttyDisplay->toplin == TOPLINE_EMPTY);
+        FALLTHROUGH;
         /*FALLTHRU*/
     case NHW_STATUS:
     case NHW_BASE:
@@ -4438,6 +4444,7 @@ tty_status_update(
     switch (fldidx) {
     case BL_RESET:
         reset_state = FORCE_RESET;
+        FALLTHROUGH;
         /*FALLTHRU*/
     case BL_FLUSH:
         if (make_things_fit(reset_state) || truncation_expected) {
@@ -4458,6 +4465,7 @@ tty_status_update(
         break;
     case BL_GOLD:
         text = decode_mixed(goldbuf, text);
+        FALLTHROUGH;
         /*FALLTHRU*/
     default:
         attrmask = (color >> 8) & 0x00FF;
@@ -4506,6 +4514,7 @@ tty_status_update(
         break;
     case BL_LEVELDESC:
         dlvl_shrinklvl = 0; /* caller is passing full length string */
+        FALLTHROUGH;
         /*FALLTHRU*/
     case BL_HUNGER:
         /* The core sends trailing blanks for some fields.
diff --git a/win/win32/mhdlg.c b/win/win32/mhdlg.c
index afa55c1c9..f190f000d 100644
--- a/win/win32/mhdlg.c
+++ b/win/win32/mhdlg.c
@@ -146,7 +146,8 @@ GetlinDlgProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
                                (WPARAM) sizeof(wbuf2), (LPARAM) wbuf2);
             NH_W2A(wbuf2, data->result, data->result_size);
 
-        /* Fall through. */
+        FALLTHROUGH;
+        /* FALLTHRU */
 
         /* cancel button was pressed */
         case IDCANCEL:
@@ -246,7 +247,8 @@ ExtCmdDlgProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
                 hWnd, IDC_EXTCMD_LIST, LB_GETCURSEL, (WPARAM) 0, (LPARAM) 0);
             if (*data->selection == LB_ERR)
                 *data->selection = -1;
-        /* Fall through. */
+            FALLTHROUGH;
+            /* FALLTHRU */
 
         /* CANCEL button ws clicked */
         case IDCANCEL: