diff --git a/core/modules/simpletest/src/BrowserTestBase.php b/core/modules/simpletest/src/BrowserTestBase.php
index f228b4e..8a44d9d 100644
--- a/core/modules/simpletest/src/BrowserTestBase.php
+++ b/core/modules/simpletest/src/BrowserTestBase.php
@@ -1010,7 +1010,7 @@ private function changeDatabasePrefix() {
    */
   protected function prepareEnvironment() {
     // Bootstrap Drupal so we can use Drupal's built in functions.
-    $this->classLoader = require DRUPAL_ROOT .'/autoload.php';
+    $this->classLoader = require __DIR__ .'/../../../../autoload.php';
     $request = Request::createFromGlobals();
     $kernel = TestRunnerKernel::createFromRequest($request, $this->classLoader);
     // TestRunnerKernel expects the working directory to be DRUPAL_ROOT.