diff --git a/include/extern.h b/include/extern.h
index 277837afb..dc3e1ffcc 100644
--- a/include/extern.h
+++ b/include/extern.h
@@ -1651,6 +1651,8 @@ extern boolean olfaction(struct permonst *);
 unsigned long cvt_adtyp_to_mseenres(uchar);
 extern void monstseesu(unsigned long);
 extern boolean resist_conflict(struct monst *);
+extern boolean mon_knows_traps(struct monst *, int);
+extern void mon_learns_traps(struct monst *, int);
 
 /* ### monmove.c ### */
 
diff --git a/include/trap.h b/include/trap.h
index e54aa9052..028f7a8b7 100644
--- a/include/trap.h
+++ b/include/trap.h
@@ -54,6 +54,7 @@ struct trap {
 
 /* unconditional traps */
 enum trap_types {
+    ALL_TRAPS    = -1, /* mon_knows_traps(), mon_learns_traps() */
     NO_TRAP      =  0,
     ARROW_TRAP   =  1,
     DART_TRAP    =  2,
diff --git a/src/makemon.c b/src/makemon.c
index 9b9e6cc04..55470c21b 100644
--- a/src/makemon.c
+++ b/src/makemon.c
@@ -1252,13 +1252,15 @@ makemon(
     else
         mtmp->female = femaleok ? rn2(2) : 0;
 
-    if (In_sokoban(&u.uz) && !mindless(ptr)) /* know about traps here */
-        mtmp->mtrapseen = (1L << (PIT - 1)) | (1L << (HOLE - 1));
+    if (In_sokoban(&u.uz) && !mindless(ptr)) { /* know about traps here */
+        mon_learns_traps(mtmp, PIT);
+        mon_learns_traps(mtmp, HOLE);
+    }
     if (Is_stronghold(&u.uz) && !mindless(ptr)) /* know about the trap doors */
-        mtmp->mtrapseen = (1L << (TRAPDOOR - 1));
+        mon_learns_traps(mtmp, TRAPDOOR);
     /* quest leader and nemesis both know about all trap types */
     if (ptr->msound == MS_LEADER || ptr->msound == MS_NEMESIS)
-        mtmp->mtrapseen = ~0;
+        mon_learns_traps(mtmp, ALL_TRAPS);
 
     place_monster(mtmp, x, y);
     mtmp->mcansee = mtmp->mcanmove = TRUE;
diff --git a/src/mon.c b/src/mon.c
index 94e292d7c..7f426134d 100644
--- a/src/mon.c
+++ b/src/mon.c
@@ -2075,7 +2075,7 @@ mfndpos(
                                 && !is_whirly(mdat) && !unsolid(mdat)))
                         && (ttmp->ttyp != ANTI_MAGIC || !resists_magm(mon))) {
                         if (!(flag & ALLOW_TRAPS)) {
-                            if (mon->mtrapseen & (1L << (ttmp->ttyp - 1)))
+                            if (mon_knows_traps(mon, ttmp->ttyp))
                                 continue;
                         }
                         info[cnt] |= ALLOW_TRAPS;
diff --git a/src/mondata.c b/src/mondata.c
index e66bfed72..9f71f2eb5 100644
--- a/src/mondata.c
+++ b/src/mondata.c
@@ -1372,4 +1372,28 @@ resist_conflict(struct monst* mtmp)
     return (rnd(20) > resist_chance);
 }
 
+/* does monster mtmp know traps of type ttyp */
+boolean
+mon_knows_traps(struct monst *mtmp, int ttyp)
+{
+    if (ttyp == ALL_TRAPS)
+        return (boolean)(mtmp->mtrapseen);
+    else if (ttyp == NO_TRAP)
+        return !(boolean)(mtmp->mtrapseen);
+    else
+        return ((mtmp->mtrapseen & (1L << (ttyp - 1))) != 0);
+}
+
+/* monster mtmp learns all traps of type ttyp */
+void
+mon_learns_traps(struct monst *mtmp, int ttyp)
+{
+    if (ttyp == ALL_TRAPS)
+        mtmp->mtrapseen = ~0L;
+    else if (ttyp == NO_TRAP)
+        mtmp->mtrapseen = 0L;
+    else
+        mtmp->mtrapseen |= (1L << (ttyp - 1));
+}
+
 /*mondata.c*/
diff --git a/src/monmove.c b/src/monmove.c
index cd41829ec..65a769d2d 100644
--- a/src/monmove.c
+++ b/src/monmove.c
@@ -45,7 +45,7 @@ mb_trapped(struct monst *mtmp, boolean canseeit)
             return TRUE;
         /* will get here if lifesaved */
     }
-    mtmp->mtrapseen |= (1 << (TRAPPED_DOOR - 1));
+    mon_learns_traps(mtmp, TRAPPED_DOOR);
     return FALSE;
 }
 
@@ -1945,7 +1945,7 @@ undesirable_disp(
 
     /* Monsters avoid a trap if they've seen that type before */
     } else if (trap && rn2(40)
-               && (mtmp->mtrapseen & (1 << (trap->ttyp - 1))) != 0) {
+               && mon_knows_traps(mtmp, trap->ttyp)) {
         return TRUE;
     }
 
diff --git a/src/muse.c b/src/muse.c
index 9b0fa86fe..3edd10bbb 100644
--- a/src/muse.c
+++ b/src/muse.c
@@ -595,7 +595,7 @@ find_defensive(struct monst* mtmp, boolean tryescape)
              * about teleport traps.
              */
             if (!noteleport_level(mtmp)
-                || !(mtmp->mtrapseen & (1 << (TELEP_TRAP - 1)))) {
+                || !mon_knows_traps(mtmp, TELEP_TRAP)) {
                 g.m.defensive = obj;
                 g.m.has_defense = (mon_has_amulet(mtmp))
                                     ? MUSE_WAN_TELEPORTATION
@@ -609,7 +609,7 @@ find_defensive(struct monst* mtmp, boolean tryescape)
                                  && !mtmp->isgd && !mtmp->ispriest))) {
             /* see WAN_TELEPORTATION case above */
             if (!noteleport_level(mtmp)
-                || !(mtmp->mtrapseen & (1 << (TELEP_TRAP - 1)))) {
+                || !mon_knows_traps(mtmp, TELEP_TRAP)) {
                 g.m.defensive = obj;
                 g.m.has_defense = MUSE_SCR_TELEPORTATION;
             }
@@ -722,7 +722,7 @@ use_defensive(struct monst* mtmp)
                 makeknown(how);
             /* monster learns that teleportation isn't useful here */
             if (noteleport_level(mtmp))
-                mtmp->mtrapseen |= (1 << (TELEP_TRAP - 1));
+                mon_learns_traps(mtmp, TELEP_TRAP);
             return 2;
         }
         if ((mon_has_amulet(mtmp) || On_W_tower_level(&u.uz)) && !rn2(3)) {
@@ -741,7 +741,7 @@ use_defensive(struct monst* mtmp)
         mbhit(mtmp, rn1(8, 6), mbhitm, bhito, otmp);
         /* monster learns that teleportation isn't useful here */
         if (noteleport_level(mtmp))
-            mtmp->mtrapseen |= (1 << (TELEP_TRAP - 1));
+            mon_learns_traps(mtmp, TELEP_TRAP);
         g.m_using = FALSE;
         return 2;
     case MUSE_SCR_TELEPORTATION: {
@@ -1350,7 +1350,7 @@ find_offensive(struct monst* mtmp)
             && !Teleport_control
             /* same hack as MUSE_WAN_TELEPORTATION_SELF */
             && (!noteleport_level(mtmp)
-                || !(mtmp->mtrapseen & (1 << (TELEP_TRAP - 1))))
+                || !mon_knows_traps(mtmp, TELEP_TRAP))
             /* do try to move hero to a more vulnerable spot */
             && (onscary(u.ux, u.uy, mtmp)
                 || (hero_behind_chokepoint(mtmp) && mon_has_friends(mtmp))
diff --git a/src/priest.c b/src/priest.c
index baf69feb2..bd0a38d7d 100644
--- a/src/priest.c
+++ b/src/priest.c
@@ -245,7 +245,7 @@ priestini(
         EPRI(priest)->shrpos.x = sx;
         EPRI(priest)->shrpos.y = sy;
         assign_level(&(EPRI(priest)->shrlevel), lvl);
-        priest->mtrapseen = ~0; /* traps are known */
+        mon_learns_traps(priest, ALL_TRAPS); /* traps are known */
         priest->mpeaceful = 1;
         priest->ispriest = 1;
         priest->isminion = 0;
@@ -691,7 +691,7 @@ mk_roamer(struct permonst *ptr, aligntyp alignment, coordxy x, coordxy y,
     EMIN(roamer)->renegade = (coaligned && !peaceful);
     roamer->ispriest = 0;
     roamer->isminion = 1;
-    roamer->mtrapseen = ~0; /* traps are known */
+    mon_learns_traps(roamer, ALL_TRAPS); /* traps are known */
     roamer->mpeaceful = peaceful;
     roamer->msleeping = 0;
     set_malign(roamer); /* peaceful may have changed */
diff --git a/src/shknam.c b/src/shknam.c
index 0a157e74c..76c6f2f85 100644
--- a/src/shknam.c
+++ b/src/shknam.c
@@ -641,7 +641,7 @@ shkinit(const struct shclass* shp, struct mkroom* sroom)
     shk->isshk = shk->mpeaceful = 1;
     set_malign(shk);
     shk->msleeping = 0;
-    shk->mtrapseen = ~0; /* we know all the traps already */
+    mon_learns_traps(shk, ALL_TRAPS); /* we know all the traps already */
     eshkp->shoproom = (schar) ((sroom - g.rooms) + ROOMOFFSET);
     sroom->resident = shk;
     eshkp->shoptype = sroom->rtype;
diff --git a/src/trap.c b/src/trap.c
index ede15c763..ac611492b 100644
--- a/src/trap.c
+++ b/src/trap.c
@@ -2552,7 +2552,7 @@ dotrap(struct trap *trap, unsigned trflags)
     }
 
     if (u.usteed)
-        u.usteed->mtrapseen |= (1 << (ttype - 1));
+        mon_learns_traps(u.usteed, ttype);
 
     /*
      * Note:
@@ -3255,7 +3255,7 @@ mintrap(struct monst *mtmp, unsigned mintrapflags)
         boolean forcetrap = ((mintrapflags & FORCETRAP) != 0);
         boolean forcebungle = (mintrapflags & FORCEBUNGLE) != 0;
         /* monster has seen such a trap before */
-        boolean already_seen = ((mtmp->mtrapseen & (1 << (tt - 1))) != 0
+        boolean already_seen = (mon_knows_traps(mtmp, tt)
                                 || (tt == HOLE && !mindless(mptr)));
 
         if (mtmp == u.usteed) {
@@ -3270,7 +3270,7 @@ mintrap(struct monst *mtmp, unsigned mintrapflags)
                 return Trap_Effect_Finished;
         }
 
-        mtmp->mtrapseen |= (1 << (tt - 1));
+        mon_learns_traps(mtmp, tt);
 
         /* Monster is aggravated by being trapped by you.
            Recognizing who made the trap isn't completely