diff -u b/core/includes/form.inc b/core/includes/form.inc
--- b/core/includes/form.inc
+++ b/core/includes/form.inc
@@ -3192,13 +3192,13 @@
 
   if (isset($element['#title']) || isset($element['#description'])) {
     // To assist screen readers, use a fieldset wrapper when possible, but
-    // fieldset legends are only compatible with the 'before' option for
-    // #title_display.
-    if (isset($element['#title_display']) && ($element['#title_display'] != 'before')) {
-      $wrapper = 'form_element';
+    // fieldset legends are only compatible with the 'before' and 'invisible'
+    // options for #title_display.
+    if (!isset($element['#title_display']) || in_array($element['#title_display'], array('before', 'invisible'))) {
+      $wrapper = 'fieldset';
     }
     else {
-      $wrapper = 'fieldset';
+      $wrapper = 'form_element';
     }
     $element['#theme_wrappers'][] = $wrapper;
   }