diff --git a/www/extras/shop/cart.js b/www/extras/shop/cart.js
index 0781d5403..da3631521 100644
--- a/www/extras/shop/cart.js
+++ b/www/extras/shop/cart.js
@@ -242,7 +242,7 @@
 
             var self   = this,
                 e      = args.elements,
-                f      = document.forms[0],
+                f      = document.getElementById('wgCartId'),
                 checks = f.sameShippingAsBilling,
                 sameChange;