diff --git a/core/js/js.js b/core/js/js.js
index 7e8ca6164c..e3941fba6d 100644
--- a/core/js/js.js
+++ b/core/js/js.js
@@ -297,7 +297,10 @@ function object(o) {
  * Fills height of window. (more precise than height: 100%;)
  */
 function fillHeight(selector) {
-	var height = parseFloat($(window).height())-parseFloat(selector.css('top'));
+	if (selector.length == 0) {
+		return;
+	}
+	var height = parseFloat($(window).height())-selector.offset().top;
 	selector.css('height', height + 'px');
 	if(selector.outerHeight() > selector.height())
 		selector.css('height', height-(selector.outerHeight()-selector.height()) + 'px');
@@ -307,8 +310,11 @@ function fillHeight(selector) {
  * Fills height and width of window. (more precise than height: 100%; or width: 100%;)
  */
 function fillWindow(selector) {
+	if (selector.length == 0) {
+		return;
+	}
 	fillHeight(selector);
-	var width = parseFloat($(window).width())-parseFloat(selector.css('left'));
+	var width = parseFloat($(window).width())-selector.offset().left;
 	selector.css('width', width + 'px');
 	if(selector.outerWidth() > selector.width())
 		selector.css('width', width-(selector.outerWidth()-selector.width()) + 'px');