diff --git a/ui/jquery.ui.position.js b/ui/jquery.ui.position.js
index aa9881cffc..deacedbcc5 100644
--- a/ui/jquery.ui.position.js
+++ b/ui/jquery.ui.position.js
@@ -37,7 +37,8 @@ $.fn.position = function( options ) {
 		targetWidth = target.width();
 		targetHeight = target.height();
 		basePosition = { top: 0, left: 0 };
-	} else if ( targetElem.scrollTo && targetElem.document ) {
+	// TODO: use $.isWindow() in 1.9
+	} else if ( targetElem.setTimeout ) {
 		targetWidth = target.width();
 		targetHeight = target.height();
 		basePosition = { top: target.scrollTop(), left: target.scrollLeft() };