diff --git a/lib/Doctrine/Common/IsolatedClassLoader.php b/lib/Doctrine/Common/IsolatedClassLoader.php
index 519a64d02..610489147 100644
--- a/lib/Doctrine/Common/IsolatedClassLoader.php
+++ b/lib/Doctrine/Common/IsolatedClassLoader.php
@@ -45,7 +45,7 @@ class IsolatedClassLoader
      * 
      * @param string $ns The namespace to use.
      */
-    public function __construct($ns)
+    public function __construct($ns = null)
     {
         $this->_namespace = $ns;
     }
@@ -96,11 +96,7 @@ class IsolatedClassLoader
      */
     public function loadClass($className)
     {
-        /*if (class_exists($className, false) || interface_exists($className, false)) {
-            return false;
-        }*/
-
-        if (strpos($className, $this->_namespace.$this->_namespaceSeparator) !== 0) {
+        if ($this->_namespace && strpos($className, $this->_namespace.$this->_namespaceSeparator) !== 0) {
             return false;
         }