diff --git a/core/includes/form.inc b/core/includes/form.inc
index c98826a..95c424b 100644
--- a/core/includes/form.inc
+++ b/core/includes/form.inc
@@ -206,7 +206,7 @@ function template_preprocess_fieldset(&$variables) {
   $variables['legend']['attributes'] = new Attribute();
 
   // Add 'visually-hidden' class to legend span.
-  if ($element['#title_display'] == 'invisible') {
+  if (isset($element['#title_display']) && $element['#title_display'] == 'invisible') {
     $variables['legend_span']['attributes'] = new Attribute(array('class' => 'visually-hidden'));
   }
   else {