diff --git a/include/monst.h b/include/monst.h
index f1fb3b9c2..8f189b4b7 100644
--- a/include/monst.h
+++ b/include/monst.h
@@ -163,7 +163,8 @@ struct monst {
 
     Bitfield(mspotted, 1);  /* mon is currently seen by hero */
     Bitfield(mwandexp, 1);  /* mon has experience with wands */
-    /* 6 spare bits */
+    Bitfield(mgenmklev, 1); /* made by the level generation */
+    /* 5 spare bits */
 
     unsigned long mstrategy; /* for monsters with mflag3: current strategy */
 #ifdef NHSTDC
diff --git a/include/patchlevel.h b/include/patchlevel.h
index 0d814189e..d05c2226d 100644
--- a/include/patchlevel.h
+++ b/include/patchlevel.h
@@ -17,7 +17,7 @@
  * Incrementing EDITLEVEL can be used to force invalidation of old bones
  * and save files.
  */
-#define EDITLEVEL 134
+#define EDITLEVEL 135
 
 /*
  * Development status possibilities.
diff --git a/src/makemon.c b/src/makemon.c
index 4f12e12cb..6f158ee01 100644
--- a/src/makemon.c
+++ b/src/makemon.c
@@ -1295,6 +1295,7 @@ makemon(
 
     place_monster(mtmp, x, y);
     mtmp->mcansee = mtmp->mcanmove = TRUE;
+    mtmp->mgenmklev = gi.in_mklev;
     mtmp->seen_resistance = M_SEEN_NOTHING;
     mtmp->mpeaceful = (mmflags & MM_ANGRY) ? FALSE : peace_minded(ptr);
     if ((mmflags & MM_MINVIS) != 0) /* for ^G */
diff --git a/src/mon.c b/src/mon.c
index 627e673bd..c0d92e6c3 100644
--- a/src/mon.c
+++ b/src/mon.c
@@ -2391,6 +2391,8 @@ mm_2way_aggression(struct monst *magr, struct monst *mdef)
        them waking up early (e.g. because a zombie decided to attack the
        Wizard of Yendor). */
     if (zombie_maker(magr) && zombie_form(mdef->data) != NON_PM) {
+        if (magr->mgenmklev && mdef->mgenmklev)
+            return 0L;
         if (!Is_stronghold(&u.uz)
             && !unique_corpstat(magr->data) && !unique_corpstat(mdef->data))
             return (ALLOW_M | ALLOW_TM);