diff --git a/lib/OpenLayers/Util.js b/lib/OpenLayers/Util.js
index 220413f2b5..38c821e8ef 100644
--- a/lib/OpenLayers/Util.js
+++ b/lib/OpenLayers/Util.js
@@ -161,7 +161,7 @@ OpenLayers.Size.prototype = {
         var equals = false;
         if (sz != null) {
             equals = ((this.w == sz.w && this.h == sz.h) ||
-                      (isNaN(this.w) && isNaN(this.h) && isNaN(px.w) && isNaN(px.h)));
+                      (isNaN(this.w) && isNaN(this.h) && isNaN(sz.w) && isNaN(sz.h)));
         }
         return equals;
     },