diff --git a/js/game.js b/js/game.js
index b6072dc..466b6dc 100644
--- a/js/game.js
+++ b/js/game.js
@@ -116,6 +116,8 @@ export class Tile {
 
         if (this.toolbelt) {
             for (let item of this.toolbelt) {
+                if (! item)
+                    continue;
                 let item_type = TILE_TYPES[item];
                 if (item_type.item_slide_ignores && item_type.item_slide_ignores.has(name))
                     return true;