diff --git a/include/monst.h b/include/monst.h
index ecb1391aa..d0cc55230 100644
--- a/include/monst.h
+++ b/include/monst.h
@@ -64,7 +64,6 @@ enum m_ap_types {
 #define MON_ENDGAME_FREE 0x20
 #define MON_ENDGAME_MIGR 0x40
 #define MON_OBLITERATE   0x80
-#define MSTATE_MASK      0xFF
 
 #define M_AP_TYPMASK  0x7
 #define M_AP_F_DKNOWN 0x8
@@ -250,7 +249,7 @@ struct monst {
 
 #define mon_perma_blind(mon) (!mon->mcansee && !mon->mblinded)
 
-#define mon_offmap(mon) (((mon)->mstate & (MON_DETACH|MON_MIGRATING|MON_LIMBO|MON_OFFMAP)) != 0)
+#define mon_offmap(mon) ((mon)->mstate != MON_FLOOR)
 
 /* Get the maximum difficulty monsters that can currently be generated,
    given the current level difficulty and the hero's level. */
diff --git a/src/cmd.c b/src/cmd.c
index 941d71822..179e55480 100644
--- a/src/cmd.c
+++ b/src/cmd.c
@@ -1057,7 +1057,7 @@ makemap_unmakemon(struct monst *mtmp, boolean migratory)
            monsters won't get out of sync; it is not on the map but
            mongone() -> m_detach() -> mon_leaving_level() copes with that */
         mtmp->mstate |= MON_OFFMAP;
-        mtmp->mstate &= ~(MON_MIGRATING | MON_LIMBO);
+        mtmp->mstate &= ~(MON_MIGRATING | MON_LIMBO | MON_ENDGAME_MIGR);
         mtmp->nmon = fmon;
         fmon = mtmp;
     }
diff --git a/src/mhitm.c b/src/mhitm.c
index 30d96fe16..33b9f8548 100644
--- a/src/mhitm.c
+++ b/src/mhitm.c
@@ -1048,8 +1048,8 @@ mdamagem(
 
     if (mhitm_knockback(magr, mdef, mattk, &mhm.hitflags,
                         (MON_WEP(magr) != 0))
-        && ((mhm.hitflags & (M_ATTK_DEF_DIED|M_ATTK_HIT)) != 0
-            || (mdef->mstate & (MON_DETACH|MON_MIGRATING|MON_LIMBO)) != 0))
+        && ((mhm.hitflags & (M_ATTK_DEF_DIED | M_ATTK_HIT)) != 0
+            || mon_offmap(mdef)))
         return mhm.hitflags;
 
     if (mhm.done)
diff --git a/src/mon.c b/src/mon.c
index 98e9e9375..80217b37b 100644
--- a/src/mon.c
+++ b/src/mon.c
@@ -237,9 +237,9 @@ mon_sanity_check(void)
         } else if (mtmp->wormno) {
             sanity_check_worm(mtmp);
 
-        /* TODO: figure out which other bits shouldn't be set for 'fmon' */
-        } else if ((mtmp->mstate & (MON_DETACH | MON_MIGRATING | MON_LIMBO))
-                   != 0) {
+        /* some temp mstate bits can be expected for a mon on fmon, as part of
+           removing it, but DEADMONSTER check above should skip those. */
+        } else if (mon_offmap(mtmp)) {
             impossible("floor mon (%s) with mstate set to 0x%08lx",
                        fmt_ptr((genericptr_t) mtmp), mtmp->mstate);
         }
@@ -267,10 +267,9 @@ mon_sanity_check(void)
     for (mtmp = gm.migrating_mons; mtmp; mtmp = mtmp->nmon) {
         sanity_check_single_mon(mtmp, FALSE, "migr");
 
-        /* TODO: figure out which other bits could or shouldn't be set
-         * when migrating */
-        if ((mtmp->mstate & (MON_DETACH)) != 0
-            || (mtmp->mstate & (MON_MIGRATING | MON_LIMBO)) == 0)
+        if ((mtmp->mstate
+             & ~(MON_MIGRATING | MON_LIMBO | MON_ENDGAME_MIGR)) != 0L
+            || !(mtmp->mstate & MON_MIGRATING))
             impossible("migrating mon (%s) with mstate set to 0x%08lx",
                        fmt_ptr((genericptr_t) mtmp), mtmp->mstate);
     }
diff --git a/src/steed.c b/src/steed.c
index 4947ddeac..1db6b2db5 100644
--- a/src/steed.c
+++ b/src/steed.c
@@ -873,8 +873,7 @@ place_monster(struct monst* mon, coordxy x, coordxy y)
     }
     mon->mx = x, mon->my = y;
     gl.level.monsters[x][y] = mon;
-    mon->mstate &= ~(MON_OFFMAP | MON_MIGRATING | MON_LIMBO | MON_BUBBLEMOVE
-                     | MON_ENDGAME_FREE | MON_ENDGAME_MIGR);
+    mon->mstate = MON_FLOOR;
 }
 
 /*steed.c*/