diff --git a/core/modules/system/src/Tests/Session/SessionAuthenticationTest.php b/core/modules/system/src/Tests/Session/SessionAuthenticationTest.php
index a2a49e5..dcee4f8 100644
--- a/core/modules/system/src/Tests/Session/SessionAuthenticationTest.php
+++ b/core/modules/system/src/Tests/Session/SessionAuthenticationTest.php
@@ -125,13 +125,23 @@ public function testBasicAuthNoSession() {
     // sustaining the session.
     $this->basicAuthGet($no_cookie_url, $this->user->getUsername(), $this->user->pass_raw);
     $this->assertResponse(200, 'The user is successfully authenticated using basic authentication.');
-    $this->assertNull($this->cookies, 'No cookie is set on a route protected with basic authentication.');
+    $this->assertEqual($this->getSetCookieCount(), 0, 'No cookie is set on a route protected with basic authentication.');
 
     // On the other hand, authenticating using Cookie sets a cookie.
     $edit = ['name' => $this->user->getUsername(), 'pass' => $this->user->pass_raw];
     $this->drupalPostForm($cookie_url, $edit, t('Log in'));
     $this->assertResponse(200, 'The user is successfully authenticated using cookie authentication.');
-    $this->assertNotNull($this->cookies, 'A cookie is set on a route protected with cookie authentication.');
+    $this->assertEqual($this->getSetCookieCount(), 1, 'A cookie is set on a route protected with cookie authentication.');
+  }
+
+  /**
+   * Returns the number of cookies that were set in the last request.
+   *
+   * @return int
+   *   The number of cookies that were set.
+   */
+  protected function getSetCookieCount() {
+    return count(preg_grep('/^Set-Cookie: ([^=]+)=(.+)/', $this->headers));
   }
 
 }