diff --git a/src/Symfony/Component/Messenger/Bridge/Amqp/Transport/AmqpFactory.php b/src/Symfony/Component/Messenger/Bridge/Amqp/Transport/AmqpFactory.php
index 6ce1bdc4da..47d8487c29 100644
--- a/src/Symfony/Component/Messenger/Bridge/Amqp/Transport/AmqpFactory.php
+++ b/src/Symfony/Component/Messenger/Bridge/Amqp/Transport/AmqpFactory.php
@@ -33,4 +33,7 @@ class AmqpFactory
         return new \AMQPExchange($channel);
     }
 }
-class_alias(AmqpFactory::class, \Symfony\Component\Messenger\Transport\AmqpExt\AmqpFactory::class);
+
+if (!class_exists(\Symfony\Component\Messenger\Transport\AmqpExt\AmqpFactory::class, false)) {
+    class_alias(AmqpFactory::class, \Symfony\Component\Messenger\Transport\AmqpExt\AmqpFactory::class);
+}
diff --git a/src/Symfony/Component/Messenger/Bridge/Amqp/Transport/AmqpReceivedStamp.php b/src/Symfony/Component/Messenger/Bridge/Amqp/Transport/AmqpReceivedStamp.php
index dd4656e809..b661cd8da9 100644
--- a/src/Symfony/Component/Messenger/Bridge/Amqp/Transport/AmqpReceivedStamp.php
+++ b/src/Symfony/Component/Messenger/Bridge/Amqp/Transport/AmqpReceivedStamp.php
@@ -37,4 +37,7 @@ class AmqpReceivedStamp implements NonSendableStampInterface
         return $this->queueName;
     }
 }
-class_alias(AmqpReceivedStamp::class, \Symfony\Component\Messenger\Transport\AmqpExt\AmqpReceivedStamp::class);
+
+if (!class_exists(\Symfony\Component\Messenger\Transport\AmqpExt\AmqpReceivedStamp::class, false)) {
+    class_alias(AmqpReceivedStamp::class, \Symfony\Component\Messenger\Transport\AmqpExt\AmqpReceivedStamp::class);
+}
diff --git a/src/Symfony/Component/Messenger/Bridge/Amqp/Transport/AmqpReceiver.php b/src/Symfony/Component/Messenger/Bridge/Amqp/Transport/AmqpReceiver.php
index 009e7be8d5..0639e80b35 100644
--- a/src/Symfony/Component/Messenger/Bridge/Amqp/Transport/AmqpReceiver.php
+++ b/src/Symfony/Component/Messenger/Bridge/Amqp/Transport/AmqpReceiver.php
@@ -136,4 +136,7 @@ class AmqpReceiver implements ReceiverInterface, MessageCountAwareInterface
         return $amqpReceivedStamp;
     }
 }
-class_alias(AmqpReceiver::class, \Symfony\Component\Messenger\Transport\AmqpExt\AmqpReceiver::class);
+
+if (!class_exists(\Symfony\Component\Messenger\Transport\AmqpExt\AmqpReceiver::class, false)) {
+    class_alias(AmqpReceiver::class, \Symfony\Component\Messenger\Transport\AmqpExt\AmqpReceiver::class);
+}
diff --git a/src/Symfony/Component/Messenger/Bridge/Amqp/Transport/AmqpSender.php b/src/Symfony/Component/Messenger/Bridge/Amqp/Transport/AmqpSender.php
index a77268bd05..2ceb965e1d 100644
--- a/src/Symfony/Component/Messenger/Bridge/Amqp/Transport/AmqpSender.php
+++ b/src/Symfony/Component/Messenger/Bridge/Amqp/Transport/AmqpSender.php
@@ -75,4 +75,7 @@ class AmqpSender implements SenderInterface
         return $envelope;
     }
 }
-class_alias(AmqpSender::class, \Symfony\Component\Messenger\Transport\AmqpExt\AmqpSender::class);
+
+if (!class_exists(\Symfony\Component\Messenger\Transport\AmqpExt\AmqpSender::class, false)) {
+    class_alias(AmqpSender::class, \Symfony\Component\Messenger\Transport\AmqpExt\AmqpSender::class);
+}
diff --git a/src/Symfony/Component/Messenger/Bridge/Amqp/Transport/AmqpStamp.php b/src/Symfony/Component/Messenger/Bridge/Amqp/Transport/AmqpStamp.php
index 7d013974cc..a2b2254927 100644
--- a/src/Symfony/Component/Messenger/Bridge/Amqp/Transport/AmqpStamp.php
+++ b/src/Symfony/Component/Messenger/Bridge/Amqp/Transport/AmqpStamp.php
@@ -74,4 +74,7 @@ final class AmqpStamp implements NonSendableStampInterface
         );
     }
 }
-class_alias(AmqpStamp::class, \Symfony\Component\Messenger\Transport\AmqpExt\AmqpStamp::class);
+
+if (!class_exists(\Symfony\Component\Messenger\Transport\AmqpExt\AmqpStamp::class, false)) {
+    class_alias(AmqpStamp::class, \Symfony\Component\Messenger\Transport\AmqpExt\AmqpStamp::class);
+}
diff --git a/src/Symfony/Component/Messenger/Bridge/Amqp/Transport/AmqpTransport.php b/src/Symfony/Component/Messenger/Bridge/Amqp/Transport/AmqpTransport.php
index 030046851f..f3e7a7ce04 100644
--- a/src/Symfony/Component/Messenger/Bridge/Amqp/Transport/AmqpTransport.php
+++ b/src/Symfony/Component/Messenger/Bridge/Amqp/Transport/AmqpTransport.php
@@ -92,4 +92,7 @@ class AmqpTransport implements TransportInterface, SetupableTransportInterface,
         return $this->sender = new AmqpSender($this->connection, $this->serializer);
     }
 }
-class_alias(AmqpTransport::class, \Symfony\Component\Messenger\Transport\AmqpExt\AmqpTransport::class);
+
+if (!class_exists(\Symfony\Component\Messenger\Transport\AmqpExt\AmqpTransport::class, false)) {
+    class_alias(AmqpTransport::class, \Symfony\Component\Messenger\Transport\AmqpExt\AmqpTransport::class);
+}
diff --git a/src/Symfony/Component/Messenger/Bridge/Amqp/Transport/AmqpTransportFactory.php b/src/Symfony/Component/Messenger/Bridge/Amqp/Transport/AmqpTransportFactory.php
index 6743e192f7..420cf7a22c 100644
--- a/src/Symfony/Component/Messenger/Bridge/Amqp/Transport/AmqpTransportFactory.php
+++ b/src/Symfony/Component/Messenger/Bridge/Amqp/Transport/AmqpTransportFactory.php
@@ -32,4 +32,7 @@ class AmqpTransportFactory implements TransportFactoryInterface
         return 0 === strpos($dsn, 'amqp://') || 0 === strpos($dsn, 'amqps://');
     }
 }
-class_alias(AmqpTransportFactory::class, \Symfony\Component\Messenger\Transport\AmqpExt\AmqpTransportFactory::class);
+
+if (!class_exists(\Symfony\Component\Messenger\Transport\AmqpExt\AmqpTransportFactory::class, false)) {
+    class_alias(AmqpTransportFactory::class, \Symfony\Component\Messenger\Transport\AmqpExt\AmqpTransportFactory::class);
+}
diff --git a/src/Symfony/Component/Messenger/Bridge/Amqp/Transport/Connection.php b/src/Symfony/Component/Messenger/Bridge/Amqp/Transport/Connection.php
index 5b21388915..4aed8831b5 100644
--- a/src/Symfony/Component/Messenger/Bridge/Amqp/Transport/Connection.php
+++ b/src/Symfony/Component/Messenger/Bridge/Amqp/Transport/Connection.php
@@ -588,4 +588,7 @@ class Connection
         return (null !== $amqpStamp ? $amqpStamp->getRoutingKey() : null) ?? $this->getDefaultPublishRoutingKey();
     }
 }
-class_alias(Connection::class, \Symfony\Component\Messenger\Transport\AmqpExt\Connection::class);
+
+if (!class_exists(\Symfony\Component\Messenger\Transport\AmqpExt\Connection::class, false)) {
+    class_alias(Connection::class, \Symfony\Component\Messenger\Transport\AmqpExt\Connection::class);
+}
diff --git a/src/Symfony/Component/Messenger/Bridge/Doctrine/Transport/Connection.php b/src/Symfony/Component/Messenger/Bridge/Doctrine/Transport/Connection.php
index b7c99a23bf..c4b398aa43 100644
--- a/src/Symfony/Component/Messenger/Bridge/Doctrine/Transport/Connection.php
+++ b/src/Symfony/Component/Messenger/Bridge/Doctrine/Transport/Connection.php
@@ -445,4 +445,7 @@ class Connection implements ResetInterface
         }
     }
 }
-class_alias(Connection::class, \Symfony\Component\Messenger\Transport\Doctrine\Connection::class);
+
+if (!class_exists(\Symfony\Component\Messenger\Transport\Doctrine\Connection::class, false)) {
+    class_alias(Connection::class, \Symfony\Component\Messenger\Transport\Doctrine\Connection::class);
+}
diff --git a/src/Symfony/Component/Messenger/Bridge/Doctrine/Transport/DoctrineReceivedStamp.php b/src/Symfony/Component/Messenger/Bridge/Doctrine/Transport/DoctrineReceivedStamp.php
index 6ec3389ab6..7f0dee1a99 100644
--- a/src/Symfony/Component/Messenger/Bridge/Doctrine/Transport/DoctrineReceivedStamp.php
+++ b/src/Symfony/Component/Messenger/Bridge/Doctrine/Transport/DoctrineReceivedStamp.php
@@ -30,4 +30,7 @@ class DoctrineReceivedStamp implements NonSendableStampInterface
         return $this->id;
     }
 }
-class_alias(DoctrineReceivedStamp::class, \Symfony\Component\Messenger\Transport\Doctrine\DoctrineReceivedStamp::class);
+
+if (!class_exists(\Symfony\Component\Messenger\Transport\Doctrine\DoctrineReceivedStamp::class, false)) {
+    class_alias(DoctrineReceivedStamp::class, \Symfony\Component\Messenger\Transport\Doctrine\DoctrineReceivedStamp::class);
+}
diff --git a/src/Symfony/Component/Messenger/Bridge/Doctrine/Transport/DoctrineReceiver.php b/src/Symfony/Component/Messenger/Bridge/Doctrine/Transport/DoctrineReceiver.php
index ca00b52a5b..de1fd53c7c 100644
--- a/src/Symfony/Component/Messenger/Bridge/Doctrine/Transport/DoctrineReceiver.php
+++ b/src/Symfony/Component/Messenger/Bridge/Doctrine/Transport/DoctrineReceiver.php
@@ -171,4 +171,7 @@ class DoctrineReceiver implements ReceiverInterface, MessageCountAwareInterface,
         );
     }
 }
-class_alias(DoctrineReceiver::class, \Symfony\Component\Messenger\Transport\Doctrine\DoctrineReceiver::class);
+
+if (!class_exists(\Symfony\Component\Messenger\Transport\Doctrine\DoctrineReceiver::class, false)) {
+    class_alias(DoctrineReceiver::class, \Symfony\Component\Messenger\Transport\Doctrine\DoctrineReceiver::class);
+}
diff --git a/src/Symfony/Component/Messenger/Bridge/Doctrine/Transport/DoctrineSender.php b/src/Symfony/Component/Messenger/Bridge/Doctrine/Transport/DoctrineSender.php
index f5612f30f0..490955dd2a 100644
--- a/src/Symfony/Component/Messenger/Bridge/Doctrine/Transport/DoctrineSender.php
+++ b/src/Symfony/Component/Messenger/Bridge/Doctrine/Transport/DoctrineSender.php
@@ -55,4 +55,7 @@ class DoctrineSender implements SenderInterface
         return $envelope->with(new TransportMessageIdStamp($id));
     }
 }
-class_alias(DoctrineSender::class, \Symfony\Component\Messenger\Transport\Doctrine\DoctrineSender::class);
+
+if (!class_exists(\Symfony\Component\Messenger\Transport\Doctrine\DoctrineSender::class, false)) {
+    class_alias(DoctrineSender::class, \Symfony\Component\Messenger\Transport\Doctrine\DoctrineSender::class);
+}
diff --git a/src/Symfony/Component/Messenger/Bridge/Doctrine/Transport/DoctrineTransport.php b/src/Symfony/Component/Messenger/Bridge/Doctrine/Transport/DoctrineTransport.php
index 9982d343e3..97bc6fac3f 100644
--- a/src/Symfony/Component/Messenger/Bridge/Doctrine/Transport/DoctrineTransport.php
+++ b/src/Symfony/Component/Messenger/Bridge/Doctrine/Transport/DoctrineTransport.php
@@ -129,4 +129,7 @@ class DoctrineTransport implements TransportInterface, SetupableTransportInterfa
         return $this->sender = new DoctrineSender($this->connection, $this->serializer);
     }
 }
-class_alias(DoctrineTransport::class, \Symfony\Component\Messenger\Transport\Doctrine\DoctrineTransport::class);
+
+if (!class_exists(\Symfony\Component\Messenger\Transport\Doctrine\DoctrineTransport::class, false)) {
+    class_alias(DoctrineTransport::class, \Symfony\Component\Messenger\Transport\Doctrine\DoctrineTransport::class);
+}
diff --git a/src/Symfony/Component/Messenger/Bridge/Doctrine/Transport/DoctrineTransportFactory.php b/src/Symfony/Component/Messenger/Bridge/Doctrine/Transport/DoctrineTransportFactory.php
index 27759ec3b0..0cda9a35ea 100644
--- a/src/Symfony/Component/Messenger/Bridge/Doctrine/Transport/DoctrineTransportFactory.php
+++ b/src/Symfony/Component/Messenger/Bridge/Doctrine/Transport/DoctrineTransportFactory.php
@@ -62,4 +62,7 @@ class DoctrineTransportFactory implements TransportFactoryInterface
         return 0 === strpos($dsn, 'doctrine://');
     }
 }
-class_alias(DoctrineTransportFactory::class, \Symfony\Component\Messenger\Transport\Doctrine\DoctrineTransportFactory::class);
+
+if (!class_exists(\Symfony\Component\Messenger\Transport\Doctrine\DoctrineTransportFactory::class, false)) {
+    class_alias(DoctrineTransportFactory::class, \Symfony\Component\Messenger\Transport\Doctrine\DoctrineTransportFactory::class);
+}
diff --git a/src/Symfony/Component/Messenger/Bridge/Redis/Transport/Connection.php b/src/Symfony/Component/Messenger/Bridge/Redis/Transport/Connection.php
index 737b24e66f..0e5bdfb935 100644
--- a/src/Symfony/Component/Messenger/Bridge/Redis/Transport/Connection.php
+++ b/src/Symfony/Component/Messenger/Bridge/Redis/Transport/Connection.php
@@ -497,4 +497,7 @@ class Connection
         }
     }
 }
-class_alias(Connection::class, \Symfony\Component\Messenger\Transport\RedisExt\Connection::class);
+
+if (!class_exists(\Symfony\Component\Messenger\Transport\RedisExt\Connection::class, false)) {
+    class_alias(Connection::class, \Symfony\Component\Messenger\Transport\RedisExt\Connection::class);
+}
diff --git a/src/Symfony/Component/Messenger/Bridge/Redis/Transport/RedisReceivedStamp.php b/src/Symfony/Component/Messenger/Bridge/Redis/Transport/RedisReceivedStamp.php
index 486aa58dfd..3469f69461 100644
--- a/src/Symfony/Component/Messenger/Bridge/Redis/Transport/RedisReceivedStamp.php
+++ b/src/Symfony/Component/Messenger/Bridge/Redis/Transport/RedisReceivedStamp.php
@@ -30,4 +30,7 @@ class RedisReceivedStamp implements NonSendableStampInterface
         return $this->id;
     }
 }
-class_alias(RedisReceivedStamp::class, \Symfony\Component\Messenger\Transport\RedisExt\RedisReceivedStamp::class);
+
+if (!class_exists(\Symfony\Component\Messenger\Transport\RedisExt\RedisReceivedStamp::class, false)) {
+    class_alias(RedisReceivedStamp::class, \Symfony\Component\Messenger\Transport\RedisExt\RedisReceivedStamp::class);
+}
diff --git a/src/Symfony/Component/Messenger/Bridge/Redis/Transport/RedisReceiver.php b/src/Symfony/Component/Messenger/Bridge/Redis/Transport/RedisReceiver.php
index 0c51d15163..89f14c4307 100644
--- a/src/Symfony/Component/Messenger/Bridge/Redis/Transport/RedisReceiver.php
+++ b/src/Symfony/Component/Messenger/Bridge/Redis/Transport/RedisReceiver.php
@@ -86,4 +86,7 @@ class RedisReceiver implements ReceiverInterface
         return $redisReceivedStamp;
     }
 }
-class_alias(RedisReceiver::class, \Symfony\Component\Messenger\Transport\RedisExt\RedisReceiver::class);
+
+if (!class_exists(\Symfony\Component\Messenger\Transport\RedisExt\RedisReceiver::class, false)) {
+    class_alias(RedisReceiver::class, \Symfony\Component\Messenger\Transport\RedisExt\RedisReceiver::class);
+}
diff --git a/src/Symfony/Component/Messenger/Bridge/Redis/Transport/RedisSender.php b/src/Symfony/Component/Messenger/Bridge/Redis/Transport/RedisSender.php
index 38b2e47515..433cfe9241 100644
--- a/src/Symfony/Component/Messenger/Bridge/Redis/Transport/RedisSender.php
+++ b/src/Symfony/Component/Messenger/Bridge/Redis/Transport/RedisSender.php
@@ -47,4 +47,7 @@ class RedisSender implements SenderInterface
         return $envelope;
     }
 }
-class_alias(RedisSender::class, \Symfony\Component\Messenger\Transport\RedisExt\RedisSender::class);
+
+if (!class_exists(\Symfony\Component\Messenger\Transport\RedisExt\RedisSender::class, false)) {
+    class_alias(RedisSender::class, \Symfony\Component\Messenger\Transport\RedisExt\RedisSender::class);
+}
diff --git a/src/Symfony/Component/Messenger/Bridge/Redis/Transport/RedisTransport.php b/src/Symfony/Component/Messenger/Bridge/Redis/Transport/RedisTransport.php
index d92afdec66..88daa22c53 100644
--- a/src/Symfony/Component/Messenger/Bridge/Redis/Transport/RedisTransport.php
+++ b/src/Symfony/Component/Messenger/Bridge/Redis/Transport/RedisTransport.php
@@ -84,4 +84,7 @@ class RedisTransport implements TransportInterface, SetupableTransportInterface
         return $this->sender = new RedisSender($this->connection, $this->serializer);
     }
 }
-class_alias(RedisTransport::class, \Symfony\Component\Messenger\Transport\RedisExt\RedisTransport::class);
+
+if (!class_exists(\Symfony\Component\Messenger\Transport\RedisExt\RedisTransport::class, false)) {
+    class_alias(RedisTransport::class, \Symfony\Component\Messenger\Transport\RedisExt\RedisTransport::class);
+}
diff --git a/src/Symfony/Component/Messenger/Bridge/Redis/Transport/RedisTransportFactory.php b/src/Symfony/Component/Messenger/Bridge/Redis/Transport/RedisTransportFactory.php
index b8a340e84f..55deeb09e7 100644
--- a/src/Symfony/Component/Messenger/Bridge/Redis/Transport/RedisTransportFactory.php
+++ b/src/Symfony/Component/Messenger/Bridge/Redis/Transport/RedisTransportFactory.php
@@ -33,4 +33,7 @@ class RedisTransportFactory implements TransportFactoryInterface
         return 0 === strpos($dsn, 'redis://');
     }
 }
-class_alias(RedisTransportFactory::class, \Symfony\Component\Messenger\Transport\RedisExt\RedisTransportFactory::class);
+
+if (!class_exists(\Symfony\Component\Messenger\Transport\RedisExt\RedisTransportFactory::class, false)) {
+    class_alias(RedisTransportFactory::class, \Symfony\Component\Messenger\Transport\RedisExt\RedisTransportFactory::class);
+}