diff --git a/src/Symfony/Component/DependencyInjection/ContainerBuilder.php b/src/Symfony/Component/DependencyInjection/ContainerBuilder.php
index 87b6118798..0d63c0be39 100644
--- a/src/Symfony/Component/DependencyInjection/ContainerBuilder.php
+++ b/src/Symfony/Component/DependencyInjection/ContainerBuilder.php
@@ -770,7 +770,7 @@ class ContainerBuilder extends Container implements TaggedContainerInterface
      */
     public function register($id, $class = null)
     {
-        return $this->setDefinition(strtolower($id), new Definition($class));
+        return $this->setDefinition($id, new Definition($class));
     }
 
     /**