diff --git a/core/tests/Drupal/Tests/Core/Test/WebAssertTest.php b/core/tests/Drupal/Tests/Core/Test/WebAssertTest.php
index 57e66d6b85246c7430d88e4a039116f234d20f9d..545f7b404b0aecf92be032c6659503a263dcc4d2 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();
   }