diff --git a/ui/ui.dialog.js b/ui/ui.dialog.js
index a9c219a135..c757be8a4c 100644
--- a/ui/ui.dialog.js
+++ b/ui/ui.dialog.js
@@ -514,6 +514,7 @@ $.extend($.ui.dialog, {
 		buttons: {},
 		closeOnEscape: true,
 		closeText: 'close',
+		dialogClass: '',
 		draggable: true,
 		height: 'auto',
 		minHeight: 150,