diff --git a/lib/OpenLayers/Layer/WMS.js b/lib/OpenLayers/Layer/WMS.js
index 93fdc5816b..3984a3e6f6 100644
--- a/lib/OpenLayers/Layer/WMS.js
+++ b/lib/OpenLayers/Layer/WMS.js
@@ -8,7 +8,9 @@ OpenLayers.Layer.WMS.prototype =
         version: "1.1.1",
         request: "GetMap",
         srs: "EPSG:4326",
-        exceptions: "application/vnd.ogc.se_inimage"
+        styles: "",
+        exceptions: "application/vnd.ogc.se_inimage",
+        format: "image/jpeg"
     },
 
     /**
@@ -18,7 +20,7 @@ OpenLayers.Layer.WMS.prototype =
     */
     initialize: function(name, url, params) {
         OpenLayers.Layer.Grid.prototype.initialize.apply(this, arguments);
-        Object.extend(this.params, this.DEFAULT_PARAMS);
+        OpenLayers.Util.applyDefaults( this.params, this.DEFAULT_PARAMS );
     },    
     
     /**
diff --git a/tests/test_Layer_WMS.html b/tests/test_Layer_WMS.html
index e47f543fc9..448aca8d19 100644
--- a/tests/test_Layer_WMS.html
+++ b/tests/test_Layer_WMS.html
@@ -5,24 +5,27 @@
     var layer; 
 
     function test_01_Layer_WMS_constructor (t) {
-	    t.plan( 4 );
+	    t.plan( 6 );
 	    
-	    layer = new OpenLayers.Layer.WMS('Test Layer', "http://octo.metacarta.com/cgi-bin/mapserv", {map: '/mapdata/vmap_wms.map', layers: 'basic', format: 'image/jpeg'});
+	    layer = new OpenLayers.Layer.WMS('Test Layer', "http://octo.metacarta.com/cgi-bin/mapserv", {map: '/mapdata/vmap_wms.map', layers: 'basic', format: 'image/png'});
 	    t.ok( layer instanceof OpenLayers.Layer.WMS, "new OpenLayers.Layer.WMS returns object" );
 	    t.eq( layer.name, "Test Layer", "layer.name is correct" );
 	    t.eq( layer.url, "http://octo.metacarta.com/cgi-bin/mapserv", "layer.url is correct" );
 	    t.eq( layer.params.map, "/mapdata/vmap_wms.map", "layer.params.map is correct" );
+	    t.eq( layer.params.format, "image/png", "layer.params.format is correctly overridden" );
+            t.eq( layer.params.exceptions, "application/vnd.ogc.se_inimage", 
+                                    "other default layer.params are set correctly" );
     }
     function test_02_Layer_WMS_addtile (t) {
         t.plan( 6 );
 	    layer = new OpenLayers.Layer.WMS('Test Layer', "http://octo.metacarta.com/cgi-bin/mapserv", {map: '/mapdata/vmap_wms.map', layers: 'basic', format: 'image/jpeg'});
         var pixel = new OpenLayers.Pixel(5,6);
         var tile = layer.addTile(new OpenLayers.Bounds(1,2,3,4), pixel);
-        t.eq( tile.img.src, "http://octo.metacarta.com/cgi-bin/mapserv?bbox=1,2,3,4&width=256&height=256&map=/mapdata/vmap_wms.map&layers=basic&format=image/jpeg&service=WMS&version=1.1.1&request=GetMap&srs=EPSG:4326&exceptions=application/vnd.ogc.se_inimage", "image src is created correctly via addtile" );
+        t.eq( tile.img.src, "http://octo.metacarta.com/cgi-bin/mapserv?bbox=1,2,3,4&width=256&height=256&map=/mapdata/vmap_wms.map&layers=basic&format=image/jpeg&service=WMS&version=1.1.1&request=GetMap&srs=EPSG:4326&styles=&exceptions=application/vnd.ogc.se_inimage", "image src is created correctly via addtile" );
         t.eq( tile.img.style.top, "6px", "image top is set correctly via addtile" );
         t.eq( tile.img.style.left, "5px", "image top is set correctly via addtile" );
         t.ok( layer.div.firstChild instanceof HTMLImageElement, "div first child is an image object" );
-        t.eq( layer.div.firstChild.src, "http://octo.metacarta.com/cgi-bin/mapserv?bbox=1,2,3,4&width=256&height=256&map=/mapdata/vmap_wms.map&layers=basic&format=image/jpeg&service=WMS&version=1.1.1&request=GetMap&srs=EPSG:4326&exceptions=application/vnd.ogc.se_inimage", "div first child is correct image object" );
+        t.eq( layer.div.firstChild.src, "http://octo.metacarta.com/cgi-bin/mapserv?bbox=1,2,3,4&width=256&height=256&map=/mapdata/vmap_wms.map&layers=basic&format=image/jpeg&service=WMS&version=1.1.1&request=GetMap&srs=EPSG:4326&styles=&exceptions=application/vnd.ogc.se_inimage", "div first child is correct image object" );
         var pos = tile.getPosition();
         t.eq( pos.toString(), "x=5,y=6", "Position of tile is set correctly." );
     }