diff --git a/src/Silex/Provider/Locale/LocaleListener.php b/src/Silex/Provider/Locale/LocaleListener.php
index 2463cc818ab28ea114e7627563b410e557c2ddf2..155c05ee68d608967aaa0e6f79adf0ee3e5d006e 100644
--- a/src/Silex/Provider/Locale/LocaleListener.php
+++ b/src/Silex/Provider/Locale/LocaleListener.php
@@ -33,7 +33,7 @@ class LocaleListener implements EventSubscriberInterface
     private $requestStack;
     private $requestContext;
 
-    public function __construct(Container $app, $defaultLocale = 'en', RequestStack $requestStack, RequestContext $requestContext = null)
+    public function __construct(Container $app, string $defaultLocale, RequestStack $requestStack, RequestContext $requestContext = null)
     {
         $this->app = $app;
         $this->defaultLocale = $defaultLocale;