diff --git a/tests/Functional/HttpClientTestCase.php b/tests/Functional/HttpClientTestCase.php
index 6df8a8d..f74d6fd 100644
--- a/tests/Functional/HttpClientTestCase.php
+++ b/tests/Functional/HttpClientTestCase.php
@@ -109,7 +109,7 @@ protected function createTempFile(): string
     /**
      * Delete files created with createTempFile
      */
-    protected function tearDown()
+    protected function tearDown(): void
     {
         parent::tearDown();