diff --git a/ui/jquery.ui.mouse.js b/ui/jquery.ui.mouse.js
index 8e6cb93f9..d0c82f83f 100644
--- a/ui/jquery.ui.mouse.js
+++ b/ui/jquery.ui.mouse.js
@@ -93,7 +93,7 @@ $.widget("ui.mouse", {
 
 	_mouseMove: function(event) {
 		// IE mouseup check - mouseup happened when mouse was out of window
-		if ($.browser.msie && parseInt($.browser.version, 10) < 9 && !event.button) {
+		if ($.browser.msie && !(document.documentMode >= 9) && !event.button) {
 			return this._mouseUp(event);
 		}