diff --git a/src/Symfony/Bundle/FrameworkBundle/Tests/Functional/SessionTest.php b/src/Symfony/Bundle/FrameworkBundle/Tests/Functional/SessionTest.php
index 530492ab8b4ed..2655ed644bbbc 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Tests/Functional/SessionTest.php
+++ b/src/Symfony/Bundle/FrameworkBundle/Tests/Functional/SessionTest.php
@@ -72,6 +72,8 @@ public function testFlash($config, $insulate)
     /**
      * Tests flash messages work when flashbag service is injected to the constructor.
      *
+     * @group legacy
+     * @expectedDeprecation The "session.flash_bag" service is deprecated since Symfony 5.1. Use $session->getFlashBag() instead
      * @dataProvider getConfigs
      */
     public function testFlashOnInjectedFlashbag($config, $insulate)