diff --git a/core/modules/rest/src/Tests/UpdateTest.php b/core/modules/rest/src/Tests/UpdateTest.php
index 5ef4b97..3eef1a9 100644
--- a/core/modules/rest/src/Tests/UpdateTest.php
+++ b/core/modules/rest/src/Tests/UpdateTest.php
@@ -258,9 +258,12 @@ public function testUpdateUser() {
     $this->httpRequest($account->urlInfo(), 'PATCH', $serialized, $this->defaultMimeType);
     $this->assertResponse(200);
 
-    // Verify that we can log in with the new password.
+    // Log out the user to clear the cookies used by the Guzzle client so that a
+    // log in request can be made for the changed user.
     $this->httpRequest('user/logout', 'GET');
     $this->loggedInUser = FALSE;
+
+    // Verify that we can log in with the new password.
     $account->pass_raw = $new_password;
     $this->drupalLogin($account);
   }