diff --git a/include/extern.h b/include/extern.h
index cd0613e01..982ba5ebf 100644
--- a/include/extern.h
+++ b/include/extern.h
@@ -1,4 +1,4 @@
-/* NetHack 3.7	extern.h	$NHDT-Date: 1706213788 2024/01/25 20:16:28 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.1373 $ */
+/* NetHack 3.7	extern.h	$NHDT-Date: 1707547708 2024/02/10 06:48:28 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.1381 $ */
 /* Copyright (c) Steve Creps, 1988.                               */
 /* NetHack may be freely redistributed.  See license for details. */
 
@@ -3686,6 +3686,7 @@ extern void setnotworn(struct obj *) NO_NNARGS; /* has tests for obj */
 extern void allunworn(void);
 extern struct obj *wearmask_to_obj(long);
 extern long wearslot(struct obj *) NONNULLARG1;
+extern void check_wornmask_slots(void);
 extern void mon_set_minvis(struct monst *) NONNULLARG1;
 extern void mon_adjust_speed(struct monst *, int, struct obj *) NONNULLARG1;
 extern void update_mon_extrinsics(struct monst *, struct obj *, boolean,
diff --git a/src/cmd.c b/src/cmd.c
index a337922e3..0940eb93b 100644
--- a/src/cmd.c
+++ b/src/cmd.c
@@ -1,4 +1,4 @@
-/* NetHack 3.7	cmd.c	$NHDT-Date: 1704225560 2024/01/02 19:59:20 $  $NHDT-Branch: keni-luabits2 $:$NHDT-Revision: 1.699 $ */
+/* NetHack 3.7	cmd.c	$NHDT-Date: 1707547723 2024/02/10 06:48:43 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.704 $ */
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /*-Copyright (c) Robert Patrick Rankin, 2013. */
 /* NetHack may be freely redistributed.  See license for details. */
@@ -4255,6 +4255,7 @@ you_sanity_check(void)
             impossible("sanity_check: you over monster");
     }
 
+    check_wornmask_slots();
     (void) check_invent_gold("invent");
 }
 
diff --git a/src/worn.c b/src/worn.c
index aa8f44c41..695a7d705 100644
--- a/src/worn.c
+++ b/src/worn.c
@@ -1,4 +1,4 @@
-/* NetHack 3.7	worn.c	$NHDT-Date: 1652577035 2022/05/15 01:10:35 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.84 $ */
+/* NetHack 3.7	worn.c	$NHDT-Date: 1707547726 2024/02/10 06:48:46 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.100 $ */
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /*-Copyright (c) Robert Patrick Rankin, 2013. */
 /* NetHack may be freely redistributed.  See license for details. */
@@ -13,22 +13,23 @@ static int extra_pref(struct monst *, struct obj *) NONNULLARG1;
 const struct worn {
     long w_mask;
     struct obj **w_obj;
-} worn[] = { { W_ARM, &uarm },
-             { W_ARMC, &uarmc },
-             { W_ARMH, &uarmh },
-             { W_ARMS, &uarms },
-             { W_ARMG, &uarmg },
-             { W_ARMF, &uarmf },
-             { W_ARMU, &uarmu },
-             { W_RINGL, &uleft },
-             { W_RINGR, &uright },
-             { W_WEP, &uwep },
-             { W_SWAPWEP, &uswapwep },
-             { W_QUIVER, &uquiver },
-             { W_AMUL, &uamul },
-             { W_TOOL, &ublindf },
-             { W_BALL, &uball },
-             { W_CHAIN, &uchain },
+    const char *w_what; /* for failing sanity check's feedback */
+} worn[] = { { W_ARM, &uarm, "suit" },
+             { W_ARMC, &uarmc, "cloak" },
+             { W_ARMH, &uarmh, "helmet" },
+             { W_ARMS, &uarms, "shield" },
+             { W_ARMG, &uarmg, "gloves" },
+             { W_ARMF, &uarmf, "boots" },
+             { W_ARMU, &uarmu, "shirt" },
+             { W_RINGL, &uleft, "left ring" },
+             { W_RINGR, &uright, "right ring" },
+             { W_WEP, &uwep, "weapon" },
+             { W_SWAPWEP, &uswapwep, "alternate weapon" },
+             { W_QUIVER, &uquiver, "quiver" },
+             { W_AMUL, &uamul, "amulet" },
+             { W_TOOL, &ublindf, "facewear" }, /* blindfold|towel|lenses */
+             { W_BALL, &uball, "chained ball" },
+             { W_CHAIN, &uchain, "attached chain" },
              { 0, 0 }
 };
 
@@ -251,6 +252,95 @@ wearslot(struct obj *obj)
     return res;
 }
 
+/* for 'sanity_check' option, called by you_sanity_check() */
+void
+check_wornmask_slots(void)
+{
+    /* we'll skip ball and chain here--they warrant separate sanity check;
+       at present, we also skip 'uskin' because it isn't included in worn[] */
+#define IGNORE_SLOTS (W_ART | W_ARTI | W_SADDLE | W_BALL| W_CHAIN)
+    char whybuf[BUFSZ];
+    const struct worn *wp;
+    struct obj *o, *otmp;
+    long m;
+
+    for (wp = worn; wp->w_mask; wp++) {
+        o = *wp->w_obj;
+        if (!o)
+            continue;
+        m = wp->w_mask;
+        if ((m & IGNORE_SLOTS) != 0L && (m & ~IGNORE_SLOTS) == 0L)
+            continue;
+        if ((o = *wp->w_obj) != 0) {
+            whybuf[0] = '\0';
+            /* slot pointer (uarm, uwep, &c) is populated; check that object
+               is in inventory and has the relevant owornmask bit set */
+            for (otmp = gi.invent; otmp; otmp = otmp->nobj)
+                if (otmp == o)
+                    break;
+            if (!otmp)
+                Sprintf(whybuf, "%s (%s) not found in invent",
+                        wp->w_what, fmt_ptr(o));
+            else if ((o->owornmask & m) == 0L)
+                Sprintf(whybuf, "%s bit not set in owornmask [0x%08lx]",
+                        wp->w_what, o->owornmask);
+            else if ((o->owornmask & ~(m | IGNORE_SLOTS)) != 0L)
+                Sprintf(whybuf, "%s wrong bit set in owornmask [0x%08lx]",
+                        wp->w_what, o->owornmask);
+            if (whybuf[0])
+                impossible("Worn-slot insanity: %s.", whybuf);
+        } /* o != NULL */
+
+        /* check whether any item other than the one in the slot pointer
+           claims to be worn/wielded in this slot; make this test whether
+           'o' is Null or not; [sanity_check_worn(mkobj.c) for object by
+           object checking will most likely have already caught this] */
+        for (otmp = gi.invent; otmp; otmp = otmp->nobj) {
+            if (otmp != o && (otmp->owornmask & wp->w_mask) != 0L) {
+                Sprintf(whybuf, "%s has owornmask 0x%08lx [0x%08lx bit set]",
+                        wp->w_what, otmp->owornmask, m);
+                impossible("Worn-slot insanity: %s.", whybuf);
+            }
+        }
+    }
+
+#ifdef EXTRA_SANITY_CHECKS
+    /* dual wielding: not a slot but lots of things to verify */
+    if (u.twoweap) {
+        const char *why = NULL;
+
+        if (!uwep || !uswapwep) {
+            Sprintf(whybuf, "without %s%s%s",
+                    !uwep ? "uwep" : "",
+                    (!uwep && !uswapwep) ? " and without " : "",
+                    !uswapwep ? "uswapwep" : "");
+            why = whybuf;
+        } else if (uarms)
+            why = "while wearing shield";
+        else if (uwep->oclass != WEAPON_CLASS && !is_weptool(uwep))
+            why = "uwep is not a weapon";
+        else if (is_launcher(uwep) || is_ammo(uwep) || is_missile(uwep))
+            why = "uwep is not a melee weapon";
+        else if (bimanual(uwep))
+            why = "uwep is two-handed";
+        else if (uswapwep->oclass != WEAPON_CLASS && !is_weptool(uswapwep))
+            why = "uswapwep is not a weapon";
+        else if (is_launcher(uswapwep) || is_ammo(uswapwep)
+                 || is_missile(uswapwep))
+            why = "uswapwep is not a melee weapon";
+        else if (bimanual(uswapwep))
+            why = "uswapwep is two-handed";
+        else if (!could_twoweap(gy.youmonst.data))
+            why = "without two weapon attacks";
+
+        if (why)
+            impossible("Two-weapon insanity: %s.", why);
+    }
+#endif /* EXTRA_SANITY_CHECKS */
+    return;
+#undef IGNORE_SLOTS
+} /* check_wornmask_slots() */
+
 void
 mon_set_minvis(struct monst *mon)
 {