diff --git a/core/includes/form.inc b/core/includes/form.inc
index 5634be8f92130e88b4e82c4b094b6f4788cf3796..ca5edb1bfc3a5d7e5f960d21858da624ed7c2f32 100644
--- a/core/includes/form.inc
+++ b/core/includes/form.inc
@@ -2795,10 +2795,15 @@ function theme_fieldset($variables) {
element_set_attributes($element, array('id'));
_form_set_attributes($element, array('form-wrapper'));
+ $legend_attributes = array();
+ if (isset($element['#title_display']) && $element['#title_display'] == 'invisible') {
+ $legend_attributes['class'][] = 'element-invisible';
+ }
+
$output = '