diff --git a/js/game.js b/js/game.js
index 831da5f..e961f5a 100644
--- a/js/game.js
+++ b/js/game.js
@@ -929,6 +929,11 @@ export class Level {
         this.pending_undo.push(() => cell._remove(tile));
     }
 
+    add_actor(actor) {
+        this.actors.push(actor);
+        this.pending_undo.push(() => this.actors.pop());
+    }
+
     spawn_animation(cell, name) {
         let type = TILE_TYPES[name];
         let tile = new Tile(type);
diff --git a/js/tiletypes.js b/js/tiletypes.js
index 8d29dc5..24a9cf3 100644
--- a/js/tiletypes.js
+++ b/js/tiletypes.js
@@ -532,7 +532,7 @@ const TILE_TYPES = {
                     // abort the clone
                     level.set_actor_stuck(tile, false);
                     if (level.attempt_step(tile, direction)) {
-                        level.actors.push(tile);
+                        level.add_actor(tile);
                         // FIXME add this underneath, just above the cloner
                         let new_tile = new tile.constructor(type, direction);
                         level.add_tile(new_tile, cell);