diff --git a/src/RouterInterface.php b/src/RouterInterface.php
index 3132239..addde88 100644
--- a/src/RouterInterface.php
+++ b/src/RouterInterface.php
@@ -65,7 +65,7 @@ public function dispatch(ServerRequestInterface $request) : array;
      *
      * @return RouteGroupInterface
      */
-    public function pushGroup(string $pattern, callable $callable) : RouteGroupInterface;
+    public function pushGroup(string $pattern, $callable) : RouteGroupInterface;
 
     /**
      * Removes the last route group from the array