diff --git a/lib/OpenLayers/Layer/WMS.js b/lib/OpenLayers/Layer/WMS.js
index 86d4bb3bdf..3ccdaaf1c5 100644
--- a/lib/OpenLayers/Layer/WMS.js
+++ b/lib/OpenLayers/Layer/WMS.js
@@ -64,7 +64,9 @@ OpenLayers.Layer.WMS.prototype =
         Object.extend(mergedParams, this.params);
         Object.extend(mergedParams, params);
         var obj = new OpenLayers.Layer.WMS(name, this.url, mergedParams);
-        obj.setTileSize(this.tileSize);
+        if (this.tileSize) {
+            obj.setTileSize(this.tileSize);
+        }    
         return obj;
     },