Index: field_group.module
===================================================================
diff --git a/sites/all/modules/field_group/field_group.module b/sites/all/modules/field_group/field_group.module
--- a/sites/all/modules/field_group/field_group.module	(revision 454)
+++ b/sites/all/modules/field_group/field_group.module	(working copy)
@@ -744,7 +744,7 @@
     if (!empty($group->classes)) {
       $class_attribute = 'class = "' . $group->classes . '"';
     }
-    $element['#prefix'] = '<div id="' . $element['#id'] . '"' . $class_attribute . '>';
+    $element['#prefix'] = '<div id="' . drupal_html_id($element['#id']) . '"' . $class_attribute . '>';
     if ($show_label) {
       $element['#prefix'] .= '<' . $label_element . '><span>' . check_plain(t($group->label)) . '</span></' . $label_element . '>';
     }