diff --git a/core/tests/Drupal/Tests/Core/Test/WebAssertTest.php b/core/tests/Drupal/Tests/Core/Test/WebAssertTest.php
index 2ca1e40abb0c018e86a5b3e28da4a0b0f3c858f3..bd469259cfd64fa3d6bffbe23ab0f457f62b725f 100644
--- a/core/tests/Drupal/Tests/Core/Test/WebAssertTest.php
+++ b/core/tests/Drupal/Tests/Core/Test/WebAssertTest.php
@@ -452,11 +452,11 @@ public function testEscapingAssertions(): void {
  */
 class MockClient extends AbstractBrowser {
 
-  public function setExpectedResponse(Response $response) {
+  public function setExpectedResponse(Response $response): void {
     $this->response = $response;
   }
 
-  protected function doRequest(object $request) {
+  protected function doRequest(object $request): object {
     return $this->response ?? new Response();
   }