diff --git a/library/Zend/Loader/ClassMapAutoloader.php b/library/Zend/Loader/ClassMapAutoloader.php
index 58b6378dbe2..e3201ee05aa 100644
--- a/library/Zend/Loader/ClassMapAutoloader.php
+++ b/library/Zend/Loader/ClassMapAutoloader.php
@@ -91,7 +91,7 @@ public function registerAutoloadMap($map)
             ));
         }
 
-        $this->map = array_merge($this->map, $map);
+        $this->map = $map + $this->map;
 
         if (isset($location)) {
             $this->mapsLoaded[] = $location;