diff --git a/ui/jquery.ui.menu.js b/ui/jquery.ui.menu.js
index 5e44e81c47..c0222629d5 100644
--- a/ui/jquery.ui.menu.js
+++ b/ui/jquery.ui.menu.js
@@ -389,7 +389,7 @@ $.widget( "ui.menu", {
 		}
 
 		nested = item.children( ".ui-menu" );
-		if ( nested.length && ( /^mouse/.test( event.type ) ) ) {
+		if ( nested.length && event && ( /^mouse/.test( event.type ) ) ) {
 			this._startOpening(nested);
 		}
 		this.activeMenu = item.parent();