diff --git a/src/apply.c b/src/apply.c
index 63fcdc964..12e8567ca 100644
--- a/src/apply.c
+++ b/src/apply.c
@@ -702,10 +702,10 @@ o_unleash(struct obj *otmp)
     for (mtmp = fmon; mtmp; mtmp = mtmp->nmon)
         if (mtmp->m_id == (unsigned) otmp->leashmon) {
             mtmp->mleashed = 0;
-            otmp->leashmon = 0;
-            update_inventory();
             break;
         }
+    otmp->leashmon = 0;
+    update_inventory();
 }
 
 /* mtmp is about to die, or become untame */
diff --git a/src/mkobj.c b/src/mkobj.c
index a78e0f05f..6e2954ade 100644
--- a/src/mkobj.c
+++ b/src/mkobj.c
@@ -2907,6 +2907,8 @@ objlist_sanity(struct obj *objlist, int wheretype, const char *mesg)
             insane_object(obj, ofmt0, mesg, (struct monst *) 0);
         if (obj->where == OBJ_INVENT && obj->how_lost != LOST_NONE) {
             char lostbuf[40];
+
+            /* %d: bitfield is unsigned but narrow, so promotes to int */
             Sprintf(lostbuf, "how_lost=%d obj in inventory!", obj->how_lost);
             insane_object(obj, ofmt0, lostbuf, (struct monst *) 0);
         }
@@ -2948,6 +2950,37 @@ objlist_sanity(struct obj *objlist, int wheretype, const char *mesg)
                 break;
             }
         }
+        if (obj->otyp == LEASH && obj->leashmon) {
+            char buf[BUFSZ];
+            struct monst *mtmp = find_mid(obj->leashmon, FM_FMON);
+
+            if (obj->where == OBJ_INVENT) {
+                if (!mtmp) { /* found leash with phantom mon */
+                    Sprintf(buf, "leashmon=%u no monst,",
+                            (unsigned) obj->leashmon);
+                    insane_object(obj, ofmt0, buf, (struct monst *) 0);
+                } else if (!mtmp->mleashed) { /* found leashed mon
+                                               * not flagged as leashed */
+                    Sprintf(buf, "leashmon=%u %s not leashed,",
+                            (unsigned) obj->leashmon, mon_pmname(mtmp));
+                    insane_object(obj, ofmt0, buf, (struct monst *) 0);
+                }
+            } else {
+                struct monst *mtmp2 = (obj->where == OBJ_MINVENT)
+                                      ? obj->ocarry : (struct monst *) 0;
+
+                if (mtmp) { /* found monst leashed by non-invent leash */
+                    Sprintf(buf, "leashmon:%u %s leashed by %s leash,",
+                            (unsigned) obj->leashmon,
+                            mon_pmname(mtmp), where_name(obj));
+                    insane_object(obj, ofmt0, buf, mtmp2);
+                } else { /* found non-invent leash with m_id of phantom mon */
+                    Sprintf(buf, "leashmon:%u no monst for %s leash,",
+                            (unsigned) obj->leashmon, where_name(obj));
+                    insane_object(obj, ofmt0, buf, mtmp2);
+                }
+            }
+        }
         if (obj->globby)
             check_glob(obj, mesg);
         /* temporary flags that might have been set but which should
@@ -3165,11 +3198,13 @@ init_dummyobj(struct obj *obj, short otyp, long oquan)
          /* obj->dknown = 0; */
          /* suppress known except for amulets (needed for fakes & real AoY) */
          obj->known = (obj->oclass == AMULET_CLASS)
-                       ? obj->known
+                         ? obj->known
                          /* default is "on" for types which don't use it */
                          : !objects[otyp].oc_uses_known;
          obj->quan = oquan ? oquan : 1L;
          obj->corpsenm = NON_PM; /* suppress statue and figurine details */
+         if (obj->otyp == LEASH)
+             obj->leashmon = 0; /* overloads corpsenm, avoid NON_PM */
          if (obj->otyp == BOULDER)
              obj->next_boulder = 0; /* overloads corpsenm, avoid NON_PM */
          /* but suppressing fruit details leads to "bad fruit #0" */
diff --git a/src/mon.c b/src/mon.c
index d1cdfdcd1..993cb32a6 100644
--- a/src/mon.c
+++ b/src/mon.c
@@ -214,6 +214,24 @@ sanity_check_single_mon(
             impossible("mimic%s concealed in inaccessible location: %s (%s)",
                        is_mimic ? "" : "ker", typnam, msg);
         }
+#endif
+    }
+    if (mtmp->mleashed) {
+        if (!get_mleash(mtmp))
+            impossible("monst %u: leashed but no leash for %s",
+                       mtmp->m_id, mon_pmname(mtmp));
+        else if (!mtmp->mtame)
+            impossible("monst %u: leashed but not tame %s",
+                       mtmp->m_id, mon_pmname(mtmp));
+#if 0
+        /* after hero moves, leashed mon won't necessarily pass 'm_next2u()'
+           test; 90 is farthest observed distance with expert jumping spell
+           when very slow mon is already several steps away and hero jumps in
+           opposite direction (if hero teleports, leashed mon moves adjacent
+           immediately; knockback has shorter range than magical jumping) */
+        else if (distu(mtmp->mx, mtmp->my) > 90) /*if (!m_next2u(mtmp))*/
+            impossible("monst %u: leashed but not next to you (%d)",
+                       mtmp->m_id, distu(mtmp->mx, mtmp->my));
 #endif
     }
 }
diff --git a/src/objnam.c b/src/objnam.c
index eeaefa4ef..7713a5dad 100644
--- a/src/objnam.c
+++ b/src/objnam.c
@@ -1407,11 +1407,16 @@ doname_base(
         if (obj->otyp == LEASH && obj->leashmon != 0) {
             struct monst *mlsh = find_mid(obj->leashmon, FM_FMON);
 
-            if (!mlsh) {
-                impossible("leashed monster not on this level");
-                obj->leashmon = 0;
-            } else {
+            if (mlsh && !DEADMONSTER(mlsh)) {
                 ConcatF1(bp, 0, " (attached to %s)", noit_mon_nam(mlsh));
+            } else {
+                if (mlsh) /*&& DEADMONSTER(mlsh)*/
+                    impossible("leashed %s #%u is dead",
+                               mon_pmname(mlsh), (unsigned) obj->leashmon);
+                else
+                    impossible("leashed monster #%u not found",
+                               (unsigned) obj->leashmon);
+                obj->leashmon = 0;
             }
             break;
         }
diff --git a/src/zap.c b/src/zap.c
index 2bec3f75c..127395788 100644
--- a/src/zap.c
+++ b/src/zap.c
@@ -1769,6 +1769,16 @@ poly_obj(struct obj *obj, int id)
             otmp->cursed = FALSE;
         }
     }
+    if (obj->otyp == LEASH && obj->leashmon != 0) {
+        if (otmp->otyp == LEASH) {
+            otmp->leashmon = obj->leashmon;
+            /* clear m_id before delobj(), to avoid o_unleash() by obfree() */
+            obj->leashmon = 0;
+        } else {
+            /* obfree() would do this if we didn't do it here */
+            o_unleash(obj);
+        }
+    }
 
     /* no box contents --KAA */
     if (Has_contents(otmp))