diff --git a/src/Symfony/Bundle/FrameworkBundle/Resources/config/mailer.php b/src/Symfony/Bundle/FrameworkBundle/Resources/config/mailer.php
index 7a3a95739b0f2..f1dc560ab76f8 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Resources/config/mailer.php
+++ b/src/Symfony/Bundle/FrameworkBundle/Resources/config/mailer.php
@@ -45,7 +45,6 @@
                 tagged_iterator('mailer.transport_factory'),
             ])
 
-        ->set('mailer.default_transport', TransportInterface::class)
         ->alias('mailer.default_transport', 'mailer.transports')
         ->alias(TransportInterface::class, 'mailer.default_transport')