diff --git a/multiupload_filefield_widget.module b/multiupload_filefield_widget.module
index 2e2b387..1482ceb 100644
--- a/multiupload_filefield_widget.module
+++ b/multiupload_filefield_widget.module
@@ -45,7 +45,9 @@ function mfw_managed_file_process($element, &$form_state, &$form) {
   $element = file_managed_file_process($element, $form_state, $form);
   $element['upload']['#attributes'] = array('multiple' => 'multiple');
   $element['upload']['#name'] = 'files_' . implode('_', $element['#parents']) . '[]';
-  $element['upload']['#attached']['js'][0]['data']['mfw'] = $element['upload']['#attached']['js'][0]['data']['file'];
+  if (!empty($element['upload']['#attached']['js'][0]['data']['file'])) {
+    $element['upload']['#attached']['js'][0]['data']['mfw'] = $element['upload']['#attached']['js'][0]['data']['file'];
+  }
   unset($element['upload']['#attached']['js'][0]['data']['file']);
   return $element;
 }