diff --git a/tests/Unit/StaticFileMiddlewareTest.php b/tests/Unit/StaticFileMiddlewareTest.php
index c5047d7..923b77a 100644
--- a/tests/Unit/StaticFileMiddlewareTest.php
+++ b/tests/Unit/StaticFileMiddlewareTest.php
@@ -234,7 +234,7 @@ public function testIfNoneMatch(string $body, string $contentLength, ?string $co
         self::assertSame($response, $middleware->process($request, $handler));
     }
 
-    public function testBaseDirectory()
+    public function testBaseDirectory(): void
     {
         $publicDirectory = sys_get_temp_dir();
         $requestTarget = '/';