diff --git a/lib/OpenLayers/Layer/WMS/Untiled.js b/lib/OpenLayers/Layer/WMS/Untiled.js
index dee755a86c..356b30c7e0 100644
--- a/lib/OpenLayers/Layer/WMS/Untiled.js
+++ b/lib/OpenLayers/Layer/WMS/Untiled.js
@@ -23,6 +23,10 @@ OpenLayers.Layer.WMS.Untiled.prototype =
                      },
     reproject: true,
 
+    /** the ratio of image/tile size to map size (this is the untiled buffer)
+     * @type int */
+    ratio: 2,
+
     /** @type OpenLayers.Tile.Image */
     tile: null,
     
@@ -125,16 +129,18 @@ OpenLayers.Layer.WMS.Untiled.prototype =
 
             //determine new tile bounds
             var center = bounds.getCenterLonLat();
+            var tileWidth = bounds.getWidth() * this.ratio;
+            var tileHeight = bounds.getHeight() * this.ratio;
             var tileBounds = 
-                new OpenLayers.Bounds(center.lon - bounds.getWidth(),
-                                      center.lat - bounds.getHeight(),
-                                      center.lon + bounds.getWidth(),
-                                      center.lat + bounds.getHeight());
+                new OpenLayers.Bounds(center.lon - (tileWidth / 2),
+                                      center.lat - (tileHeight / 2),
+                                      center.lon + (tileWidth / 2),
+                                      center.lat + (tileHeight / 2));
 
             //determine new tile size
             var tileSize = this.map.getSize();
-            tileSize.w = tileSize.w * 2;
-            tileSize.h = tileSize.h * 2;
+            tileSize.w = tileSize.w * this.ratio;
+            tileSize.h = tileSize.h * this.ratio;
 
             //formulate request url string
             var url = this.getURL(tileBounds); 
@@ -156,8 +162,8 @@ OpenLayers.Layer.WMS.Untiled.prototype =
     
     getURL: function(bounds) {
         var tileSize = this.map.getSize();
-        tileSize.w = tileSize.w * 2;
-        tileSize.h = tileSize.h * 2;
+        tileSize.w = tileSize.w * this.ratio;
+        tileSize.h = tileSize.h * this.ratio;
         return this.getFullRequestString( {'BBOX': bounds.toBBOX(),
                                                   'WIDTH': tileSize.w,
                                                   'HEIGHT': tileSize.h} );