diff --git a/wp-includes/js/tinymce/mark_loaded_src.js b/wp-includes/js/tinymce/mark_loaded_src.js
index 8cec04198..2b5319267 100644
--- a/wp-includes/js/tinymce/mark_loaded_src.js
+++ b/wp-includes/js/tinymce/mark_loaded_src.js
@@ -1,5 +1,5 @@
-(function(undefined){
-	if ( undefined === tinyMCEPreInit )
+(function(){
+	if ( typeof tinyMCEPreInit === 'undefined' )
 		return;
 
 	var t = tinyMCEPreInit, baseurl = t.base, markDone = tinymce.ScriptLoader.markDone, lang = t.ref.language,