diff --git a/src/Debug/Toolbar.php b/src/Debug/Toolbar.php
index 14c599e..601bd45 100644
--- a/src/Debug/Toolbar.php
+++ b/src/Debug/Toolbar.php
@@ -20,7 +20,7 @@ class Toolbar extends BaseToolbar
      *
      * @psalm-suppress UndefinedClass
      */
-    public function prepare(?RequestInterface $request = null, ?ResponseInterface $response = null)
+    public function prepare(?RequestInterface $request = null, ?ResponseInterface $response = null): void
     {
         /**
          * @var IncomingRequest|null $request