diff --git a/src/Router/AdminRouteGenerator.php b/src/Router/AdminRouteGenerator.php
index f44c701709..ae9f2f69cd 100644
--- a/src/Router/AdminRouteGenerator.php
+++ b/src/Router/AdminRouteGenerator.php
@@ -84,7 +84,7 @@ public function __construct(
         private readonly CacheItemPoolInterface $cache,
         private readonly Filesystem $filesystem,
         private readonly string $buildDir,
-        private readonly string $defaultLocale,
+        private readonly ?string $defaultLocale,
         private readonly iterable $adminRouteControllers = [],
     ) {
     }