diff --git a/core/tests/Drupal/Tests/Listeners/DrupalStandardsListener.php b/core/tests/Drupal/Tests/Listeners/DrupalStandardsListener.php
index 913e46899a..fd15f8218b 100644
--- a/core/tests/Drupal/Tests/Listeners/DrupalStandardsListener.php
+++ b/core/tests/Drupal/Tests/Listeners/DrupalStandardsListener.php
@@ -143,7 +143,15 @@ public function checkValidCoversForTest(TestCase $test) {
   /**
    * {@inheritdoc}
    *
+   * We must mark this method as belonging to the special legacy group because
+   * it might trigger an E_USER_DEPRECATED error during coverage annotation
+   * validation. The legacy group allows symfony/phpunit-bridge to keep the
+   * deprecation notice as a warning instead of an error, which would fail the
+   * test.
+   *
    * @group legacy
+   *
+   * @see http://symfony.com/doc/current/components/phpunit_bridge.html#mark-tests-as-legacy
    */
   public function endTest(\PHPUnit_Framework_Test $test, $time) {
     // \PHPUnit_Framework_Test does not have any useful methods of its own for