diff --git a/modules/file/file.module b/modules/file/file.module
index 3d351fa..7d5aa01 100644
--- a/modules/file/file.module
+++ b/modules/file/file.module
@@ -547,7 +547,10 @@ function file_managed_file_validate(&$element, &$form_state) {
   // If referencing an existing file, only allow if there are existing
   // references. This prevents unmanaged files from being deleted if this
   // item were to be deleted.
-  $clicked_button = end($form_state['triggering_element']['#parents']);
+  $clicked_button = '';
+  if (!empty($form_state['triggering_element'])) {
+    $clicked_button = end($form_state['triggering_element']['#parents']);
+  }
   if ($clicked_button != 'remove_button' && !empty($element['fid']['#value'])) {
     if ($file = file_load($element['fid']['#value'])) {
       if ($file->status == FILE_STATUS_PERMANENT) {