diff --git a/includes/form.inc b/includes/form.inc
index c56a4fe..d3f055e 100644
--- a/includes/form.inc
+++ b/includes/form.inc
@@ -86,7 +86,7 @@ function radix_button($variables) {
   }
 
   // add a btn-primary class if submit button
-  if ($element['#parents'][0] == 'submit') {
+  if (isset($element['#parents'][0]) && ($element['#parents'][0] == 'submit')) {
     $element['#attributes']['class'][] = 'btn-primary';
   }