diff --git a/DependencyInjection/Configuration.php b/DependencyInjection/Configuration.php
index 951ac85..3954ef7 100644
--- a/DependencyInjection/Configuration.php
+++ b/DependencyInjection/Configuration.php
@@ -22,7 +22,7 @@ public function getConfigTreeBuilder()
         $rootNode
             ->children()
                 ->scalarNode('locale_provider')->defaultValue('default')->end()
-                ->scalarNode('default_locale')->isRequired(false)->end()
+                ->scalarNode('default_locale')->defaultNull()->end()
                 ->arrayNode('locales')
                     ->beforeNormalization()
                         ->ifString()