diff --git a/contents/code/spirallayout.js b/contents/code/spirallayout.js
index ea56ef105b1bc9b65d2bae934574cfb63b835ea7..57d50a3f16db2293faeba11563bada930876ed48 100644
--- a/contents/code/spirallayout.js
+++ b/contents/code/spirallayout.js
@@ -43,7 +43,7 @@ SpiralLayout.prototype.resetTileSizes = function() {
     var tileCount = this.tiles.length;
     this.tiles.length = 0;
     for (var i = 0; i < tileCount; i++) {
-        addTile();
+        this.addTile();
     }
 }