diff --git a/core/includes/form.inc b/core/includes/form.inc
index 0ef70f8..ac191fc 100644
--- a/core/includes/form.inc
+++ b/core/includes/form.inc
@@ -2831,10 +2831,15 @@ function theme_fieldset($variables) {
$element['#attributes']['aria-describedby'] = $description_id;
}
+ $legend_attributes = array();
+ if (isset($element['#title_display']) && $element['#title_display'] == 'invisible') {
+ $legend_attributes['class'][] = 'element-invisible';
+ }
+
$output = '