diff --git a/src/Symfony/Bundle/FrameworkBundle/DependencyInjection/Configuration.php b/src/Symfony/Bundle/FrameworkBundle/DependencyInjection/Configuration.php
index <HASH>..<HASH> 100644
--- a/src/Symfony/Bundle/FrameworkBundle/DependencyInjection/Configuration.php
+++ b/src/Symfony/Bundle/FrameworkBundle/DependencyInjection/Configuration.php
@@ -279,6 +279,7 @@ class Configuration implements ConfigurationInterface
                                     ->scalarNode('version')->defaultNull()->end()
                                     ->scalarNode('version_format')->defaultNull()->end()
                                     ->arrayNode('base_urls')
+                                        ->performNoDeepMerging()
                                         ->addDefaultsIfNotSet()
                                         ->defaultValue(array('http' => array(), 'ssl' => array()))
                                         ->beforeNormalization()
[FrameworkBundle] fixes unintuitive merging behavior