diff --git a/src/Illuminate/Foundation/Support/Providers/RouteServiceProvider.php b/src/Illuminate/Foundation/Support/Providers/RouteServiceProvider.php
index 323f0f32b42a..72ba1cc1abd2 100644
--- a/src/Illuminate/Foundation/Support/Providers/RouteServiceProvider.php
+++ b/src/Illuminate/Foundation/Support/Providers/RouteServiceProvider.php
@@ -85,10 +85,10 @@ protected function routes(Closure $routesCallback)
     /**
      * Register the callback that will be used to load the application's routes.
      *
-     * @param  \Closure  $routesCallback
+     * @param  \Closure|null  $routesCallback
      * @return void
      */
-    public static function loadRoutesUsing(Closure $routesCallback)
+    public static function loadRoutesUsing(?Closure $routesCallback)
     {
         self::$alwaysLoadRoutesUsing = $routesCallback;
     }