diff --git a/attack.cpp b/attack.cpp
index 088897bf..7991452b 100644
--- a/attack.cpp
+++ b/attack.cpp
@@ -761,7 +761,8 @@ EX void killMonster(cell *c, eMonster who, flagtype deathflags IS(0)) {
       drawBubble(c, 0xFFFF00, s.get_str(100), .5);
     if(m == moIvyBranch || m == moIvyHead || m == moIvyNext) {
       int qty = 0;
-      cell *c2 = c->move(c->mondir);
+      cell *c2 = proper(c, c->mondir) ? c->move(c->mondir) : nullptr;
+      if(!c2) c2 = c; /* should not happen */
       for(int i=0; i<c2->type; i++)
         if(c2->move(i)->monst == moIvyWait && c2->move(i)->mondir == c2->c.spin(i))
           qty++;
diff --git a/monstermove.cpp b/monstermove.cpp
index e4545817..774a27dc 100644
--- a/monstermove.cpp
+++ b/monstermove.cpp
@@ -931,6 +931,8 @@ EX void ivynext(cell *c) {
   cell *c2 = c;
   while(true) {
     if(c2->monst == moIvyRoot) break;
+    if(!proper(c2, c2->mondir))
+      return; /* incorrect data */
     if(!isIvy(c2->monst)) break;
     if(c2->c.mirror(c2->mondir)) cw.mirrored = !cw.mirrored;
     c2 = c2->move(c2->mondir);
@@ -1031,6 +1033,7 @@ EX void moveivy() {
         mto->monst = moIvyHead; co->monst = moIvyBranch;
         }
       }
+    else if(!proper(co, co->mondir) || !co->move(co->mondir)) ; /* should not happen */
     else if(co->move(co->mondir)->monst != moIvyRoot) {
       // shrink useless branches, but do not remove them completely (at the root)
       if(co->monst == moIvyHead) co->move(co->mondir)->monst = moIvyHead;