diff --git a/lib/OpenLayers/BaseTypes.js b/lib/OpenLayers/BaseTypes.js
index d156d61a1b..3fdd2aa2b0 100644
--- a/lib/OpenLayers/BaseTypes.js
+++ b/lib/OpenLayers/BaseTypes.js
@@ -115,7 +115,11 @@ OpenLayers.Pixel.prototype = {
     * @type OpenLayers.Pixel
     */
     offset:function(px) {
-        return this.add(px.x, px.y);                
+        var newPx = this.clone();
+        if (px) {
+            newPx = this.add(px.x, px.y);
+        }
+        return newPx;
     },
     
     /** @final @type str */