diff --git a/modules/cart/commerce_cart.module b/modules/cart/commerce_cart.module
index f75f2ff..eddf2dd 100644
--- a/modules/cart/commerce_cart.module
+++ b/modules/cart/commerce_cart.module
@@ -664,6 +664,7 @@ function commerce_cart_add_to_cart_form($form, &$form_state, $product_ids, $show
               '#options' => array_intersect_key($data['options'], drupal_map_assoc($used_options[$field_name])),
               '#default_value' => $default_product->{$field_name}[LANGUAGE_NONE][0]['value'],
               '#weight' => $data['instance']['widget']['weight'],
+              '#disabled' => count($used_options[$field_name]) == 1,
               '#ajax' => array(
                 'callback' => 'commerce_cart_add_to_cart_form_attributes_refresh',
               ),