diff --git a/src/Symfony/Component/Mailer/Mailer.php b/src/Symfony/Component/Mailer/Mailer.php
index e40e418957..260989e721 100644
--- a/src/Symfony/Component/Mailer/Mailer.php
+++ b/src/Symfony/Component/Mailer/Mailer.php
@@ -11,6 +11,7 @@
 
 namespace Symfony\Component\Mailer;
 
+use Symfony\Component\EventDispatcher\LegacyEventDispatcherProxy;
 use Symfony\Component\Mailer\Event\MessageEvent;
 use Symfony\Component\Mailer\Messenger\SendEmailMessage;
 use Symfony\Component\Mailer\Transport\TransportInterface;
@@ -31,7 +32,7 @@ final class Mailer implements MailerInterface
     {
         $this->transport = $transport;
         $this->bus = $bus;
-        $this->dispatcher = $dispatcher;
+        $this->dispatcher = LegacyEventDispatcherProxy::decorate($dispatcher);
     }
 
     public function send(RawMessage $message, Envelope $envelope = null): void