diff --git a/js/game.js b/js/game.js
index bd29d9e..10b2307 100644
--- a/js/game.js
+++ b/js/game.js
@@ -1618,7 +1618,7 @@ export class Level extends LevelInterface {
             let original_name = tile.type.name;
             // TODO check ignores here?
             if (tile.type.on_bumped) {
-                tile.type.on_bumped(tile, this, actor);
+                tile.type.on_bumped(tile, this, actor, direction);
             }
 
             // Death happens here: if a monster or block even thinks about moving into a player, or
diff --git a/js/tiletypes.js b/js/tiletypes.js
index d38ab81..96698e0 100644
--- a/js/tiletypes.js
+++ b/js/tiletypes.js
@@ -1226,10 +1226,10 @@ const TILE_TYPES = {
                 return null;
             }
         },
-        on_bumped(me, level, other) {
+        on_bumped(me, level, other, direction) {
             if (other.type.name === 'boulder') {
                 level._set_tile_prop(me, 'rolling', true);
-                level._set_tile_prop(me, 'direction', other.direction);
+                level._set_tile_prop(me, 'direction', direction);
                 level._set_tile_prop(other, 'rolling', false);
             }
         },