diff --git a/lib/OpenLayers/Map.js b/lib/OpenLayers/Map.js
index 92f5a02da5..e7910548a9 100644
--- a/lib/OpenLayers/Map.js
+++ b/lib/OpenLayers/Map.js
@@ -1469,15 +1469,13 @@ OpenLayers.Map = OpenLayers.Class({
         }
     
         if ((center != null) && (resolution != null)) {
-
-            var size = this.getSize();
-            var w_deg = size.w * resolution;
-            var h_deg = size.h * resolution;
+            var half_w_deg = (this.size.w * resolution) / 2;
+            var half_h_deg = (this.size.h * resolution) / 2;
         
-            extent = new OpenLayers.Bounds(center.lon - w_deg / 2,
-                                           center.lat - h_deg / 2,
-                                           center.lon + w_deg / 2,
-                                           center.lat + h_deg / 2);
+            extent = new OpenLayers.Bounds(center.lon - half_w_deg,
+                                           center.lat - half_h_deg,
+                                           center.lon + half_w_deg,
+                                           center.lat + half_h_deg);
         
         }
 
@@ -2318,15 +2316,15 @@ OpenLayers.Map = OpenLayers.Class({
     zoomToScale: function(scale, closest) {
         var res = OpenLayers.Util.getResolutionFromScale(scale, 
                                                          this.baseLayer.units);
-        var size = this.getSize();
-        var w_deg = size.w * res;
-        var h_deg = size.h * res;
+
+        var half_w_deg = (this.size.w * res) / 2;
+        var half_h_deg = (this.size.h * res) / 2;
         var center = this.getCachedCenter();
 
-        var extent = new OpenLayers.Bounds(center.lon - w_deg / 2,
-                                           center.lat - h_deg / 2,
-                                           center.lon + w_deg / 2,
-                                           center.lat + h_deg / 2);
+        var extent = new OpenLayers.Bounds(center.lon - half_w_deg,
+                                           center.lat - half_h_deg,
+                                           center.lon + half_w_deg,
+                                           center.lat + half_h_deg);
         this.zoomToExtent(extent, closest);
     },
     
diff --git a/tests/Map.html b/tests/Map.html
index faad0b30c7..2401ae21d6 100644
--- a/tests/Map.html
+++ b/tests/Map.html
@@ -1406,6 +1406,7 @@
         
         var m = {
             'baseLayer': { 'units': {} },
+            'size': {'w': 10, 'h': 15},
             'getSize': function() { return {'w': 10, 'h': 15}; },
             'getCachedCenter': function() { return {'lon': -5, 'lat': -25}; },
             'zoomToExtent': function(extent, closest) {