diff --git a/lib/OpenLayers/Events.js b/lib/OpenLayers/Events.js
index de83e342e8..eefa2fbc02 100644
--- a/lib/OpenLayers/Events.js
+++ b/lib/OpenLayers/Events.js
@@ -72,10 +72,12 @@ OpenLayers.Events.prototype = {
     * @return {OpenLayers.Pixel}
     */
     getMousePosition: function (evt) {
-        var offsets = Position.page(this.div); 
+        if (!this.div.offsets) {
+            this.div.offsets = Position.page(this.div);
+        }
         return new OpenLayers.Pixel(
-                        evt.clientX - offsets[0], 
-                        evt.clientY - offsets[1]); 
+                        evt.clientX - this.div.offsets[0], 
+                        evt.clientY - this.div.offsets[1]); 
     },
 
     /**
diff --git a/lib/OpenLayers/Map.js b/lib/OpenLayers/Map.js
index 920816d8bc..fafe73eb93 100644
--- a/lib/OpenLayers/Map.js
+++ b/lib/OpenLayers/Map.js
@@ -207,7 +207,7 @@ OpenLayers.Map.prototype = {
     updateSize: function() {
         this.size = new OpenLayers.Size(
                     this.div.clientWidth, this.div.clientHeight);
-        
+        this.events.div.offsets = null;
         // Workaround for the fact that hidden elements return 0 for size.
         if (this.size.w == 0 && this.size.h == 0) {
             this.size.w = parseInt(this.div.style.width);