diff --git a/lib/OpenLayers/BaseTypes.js b/lib/OpenLayers/BaseTypes.js
index 1c1306e057..edcf84db3a 100644
--- a/lib/OpenLayers/BaseTypes.js
+++ b/lib/OpenLayers/BaseTypes.js
@@ -20,7 +20,7 @@ OpenLayers.Class = {
         for (var i = 1; i < arguments.length; i++) {
             if (typeof arguments[i] == "function") {
                 var mixin = arguments[i];
-                arguments[i] = mixin.prototype;
+                arguments[i] = new mixin(OpenLayers.Class.isPrototype);
             }
             OpenLayers.Util.extend(proto, arguments[i]);