diff --git a/core/modules/simpletest/src/WebTestBase.php b/core/modules/simpletest/src/WebTestBase.php
index 5d8fd52..9397deb 100644
--- a/core/modules/simpletest/src/WebTestBase.php
+++ b/core/modules/simpletest/src/WebTestBase.php
@@ -996,7 +996,7 @@ protected function installParameters() {
           'account' => array(
             'name' => $this->rootUser->name,
             'mail' => $this->rootUser->getEmail(),
-            'pass' => $this->root_user->pass_raw,
+            'pass' => $this->rootUser->pass_raw,
           ),
           // \Drupal\Core\Render\Element\Checkboxes::valueCallback() requires
           // NULL instead of FALSE values for programmatic form submissions to