diff --git a/lib/OpenLayers/Map.js b/lib/OpenLayers/Map.js
index bd8378a10b..e545113d2a 100644
--- a/lib/OpenLayers/Map.js
+++ b/lib/OpenLayers/Map.js
@@ -1098,16 +1098,18 @@ OpenLayers.Map = OpenLayers.Class({
      * newBaseLayer - {<OpenLayers.Layer>}
      */
     setBaseLayer: function(newBaseLayer) {
-        var oldExtent = null;
-        if (this.baseLayer) {
-            oldExtent = this.baseLayer.getExtent();
-        }
-
+        
         if (newBaseLayer != this.baseLayer) {
           
-            // is newBaseLayer an already loaded layer?m
+            // ensure newBaseLayer is already loaded
             if (OpenLayers.Util.indexOf(this.layers, newBaseLayer) != -1) {
 
+                // preserve center and scale when changing base layers
+                var center = this.getCenter();
+                var newResolution = OpenLayers.Util.getResolutionFromScale(
+                    this.getScale(), newBaseLayer.units
+                );
+
                 // make the old base layer invisible 
                 if (this.baseLayer != null && !this.allOverlays) {
                     this.baseLayer.setVisibility(false);
@@ -1124,24 +1126,14 @@ OpenLayers.Map = OpenLayers.Class({
                     this.baseLayer.setVisibility(true);
                 }
 
-                //redraw all layers
-                var center = this.getCenter();
+                // recenter the map
                 if (center != null) {
-
-                    //either get the center from the old Extent or just from
-                    // the current center of the map. 
-                    var newCenter = (oldExtent) 
-                        ? oldExtent.getCenterLonLat()
-                        : center;
-
-                    //the new zoom will either come from the old Extent or 
-                    // from the current resolution of the map                                                
-                    var newZoom = (oldExtent) 
-                        ? this.getZoomForExtent(oldExtent, true)
-                        : this.getZoomForResolution(this.resolution, true);
-
+                    // new zoom level derived from old scale
+                    var newZoom = this.getZoomForResolution(
+                        newResolution || this.resolution, true
+                    );
                     // zoom and force zoom change
-                    this.setCenter(newCenter, newZoom, false, true);
+                    this.setCenter(center, newZoom, false, true);
                 }
 
                 this.events.triggerEvent("changebaselayer", {