diff --git a/modules/cart/commerce_cart.module b/modules/cart/commerce_cart.module
index e1bb9e46..f72f0a5e 100644
--- a/modules/cart/commerce_cart.module
+++ b/modules/cart/commerce_cart.module
@@ -2069,7 +2069,7 @@ function commerce_cart_add_to_cart_form($form, &$form_state, $line_item, $show_q
                 continue;
               }
 
-              if (array_key_exists('#default_value', $form['attributes'][$used_field_name])) {
+              if (isset($form['attributes'][$used_field_name]) && array_key_exists('#default_value', $form['attributes'][$used_field_name])) {
                 if ($product_wrapper->{$used_field_name}->raw() != $form['attributes'][$used_field_name]['#default_value']) {
                   continue 2;
                 }