Index: wp-includes/js/autosave.dev.js
===================================================================
--- wp-includes/js/autosave.dev.js	(revision 15757)
+++ wp-includes/js/autosave.dev.js	(working copy)
@@ -197,7 +197,7 @@
 autosave = function() {
 	// (bool) is rich editor enabled and active
 	blockSave = true;
-	var rich = (typeof tinyMCE != "undefined") && tinyMCE.activeEditor && !tinyMCE.activeEditor.isHidden(), post_data, doAutoSave, ed, origStatus, successCallback;
+	var rich = (typeof tinyMCE != "undefined") && tinyMCE.get('content') && !tinyMCE.get('content').isHidden(), post_data, doAutoSave, ed, origStatus, successCallback;
 
 	autosave_disable_buttons();