diff --git a/lib/OpenLayers/Control/MouseDefaults.js b/lib/OpenLayers/Control/MouseDefaults.js
index d43f3fb45b..6de8c3cede 100644
--- a/lib/OpenLayers/Control/MouseDefaults.js
+++ b/lib/OpenLayers/Control/MouseDefaults.js
@@ -166,29 +166,31 @@ OpenLayers.Control.MouseDefaults.prototype =
      *
      */
     zoomBoxEnd: function(evt) {
-        if (Math.abs(this.mouseDragStart.x - evt.xy.x) > 5 ||    
-            Math.abs(this.mouseDragStart.y - evt.xy.y) > 5) {   
-            var start = this.map.getLonLatFromViewPortPx( this.mouseDragStart ); 
-            var end = this.map.getLonLatFromViewPortPx( evt.xy );
-            var top = Math.max(start.lat, end.lat);
-            var bottom = Math.min(start.lat, end.lat);
-            var left = Math.min(start.lon, end.lon);
-            var right = Math.max(start.lon, end.lon);
-            var bounds = new OpenLayers.Bounds(left, bottom, right, top);
-            var zoom = this.map.getZoomForExtent(bounds);
-            this.map.setCenter(new OpenLayers.LonLat(
-              (start.lon + end.lon) / 2,
-              (start.lat + end.lat) / 2
-             ), zoom);
-        } else {
-            var end = this.map.getLonLatFromViewPortPx( evt.xy );
-            this.map.setCenter(new OpenLayers.LonLat(
-              (end.lon),
-              (end.lat)
-             ), this.map.getZoom() + 1);
-        }    
-        this.map.viewPortDiv.removeChild(document.getElementById("zoomBox"));
-        this.zoomBox = null;
+        if (this.mouseDragStart != null) {
+            if (Math.abs(this.mouseDragStart.x - evt.xy.x) > 5 ||    
+                Math.abs(this.mouseDragStart.y - evt.xy.y) > 5) {   
+                var start = this.map.getLonLatFromViewPortPx( this.mouseDragStart ); 
+                var end = this.map.getLonLatFromViewPortPx( evt.xy );
+                var top = Math.max(start.lat, end.lat);
+                var bottom = Math.min(start.lat, end.lat);
+                var left = Math.min(start.lon, end.lon);
+                var right = Math.max(start.lon, end.lon);
+                var bounds = new OpenLayers.Bounds(left, bottom, right, top);
+                var zoom = this.map.getZoomForExtent(bounds);
+                this.map.setCenter(new OpenLayers.LonLat(
+                  (start.lon + end.lon) / 2,
+                  (start.lat + end.lat) / 2
+                 ), zoom);
+            } else {
+                var end = this.map.getLonLatFromViewPortPx( evt.xy );
+                this.map.setCenter(new OpenLayers.LonLat(
+                  (end.lon),
+                  (end.lat)
+                 ), this.map.getZoom() + 1);
+            }    
+            this.map.viewPortDiv.removeChild(document.getElementById("zoomBox"));
+            this.zoomBox = null;
+       }     
     },