diff --git a/lib/OpenLayers/Layer/WMS.js b/lib/OpenLayers/Layer/WMS.js
index 9ec9ac6a77..0bf43022ae 100644
--- a/lib/OpenLayers/Layer/WMS.js
+++ b/lib/OpenLayers/Layer/WMS.js
@@ -21,13 +21,8 @@ OpenLayers.Layer.WMS.prototype =
                       format: "image/jpeg"
                      },
 
-    /** WMS layer by default is a base layer. 
-     *   If the user wishes to use a WMS as a datalayer, s/he needs only 
-     *   set this property to false.
-     * 
-     * @type Boolean
-     */
-    isBaseLayer: true,
+    /** @type Boolean */
+    isBaseLayer: null,
 
     /**
     * @constructor
@@ -52,6 +47,8 @@ OpenLayers.Layer.WMS.prototype =
                            OpenLayers.Util.upperCaseObject(this.DEFAULT_PARAMS)
                            );
         }
+        
+        this.isBaseLayer = (this.params.TRANSPARENT != "true");
     },    
 
     /**
diff --git a/tests/test_Layer_WMS.html b/tests/test_Layer_WMS.html
index 0dd71d2b6b..e52965590b 100644
--- a/tests/test_Layer_WMS.html
+++ b/tests/test_Layer_WMS.html
@@ -98,12 +98,22 @@
 
     function test_05_Layer_WMS_isBaseLayer(t) {
 
-        t.plan(1);
+        t.plan(2);
         
         var url = "http://octo.metacarta.com/cgi-bin/mapserv";
         layer = new OpenLayers.Layer.WMS(name, url, params);
 
         t.ok( layer.isBaseLayer, "baselayer is true by default");
+
+        var newParams = Object.extend(new Object(), params);
+        newParams.transparent = "true";
+        layer = new OpenLayers.Layer.WMS(name, url, newParams);
+        
+
+        t.ok( !layer.isBaseLayer, "baselayer is false when transparent is set to true");
+
+
+
     }
 
     function test_06_Layer_WMS_mergeNewParams (t) {