diff --git a/src/Symfony/Component/Messenger/Tests/Transport/InMemoryTransportTest.php b/src/Symfony/Component/Messenger/Tests/Transport/InMemoryTransportTest.php
index 22149f8a39..6fddc3fbbc 100644
--- a/src/Symfony/Component/Messenger/Tests/Transport/InMemoryTransportTest.php
+++ b/src/Symfony/Component/Messenger/Tests/Transport/InMemoryTransportTest.php
@@ -13,6 +13,7 @@ namespace Symfony\Component\Messenger\Tests\Transport;
 
 use PHPUnit\Framework\TestCase;
 use Symfony\Component\Messenger\Envelope;
+use Symfony\Component\Messenger\Tests\Fixtures\AnEnvelopeStamp;
 use Symfony\Component\Messenger\Transport\InMemoryTransport;
 
 /**
@@ -50,6 +51,19 @@ class InMemoryTransportTest extends TestCase
         $this->assertSame([], $this->transport->get());
     }
 
+    public function testAcknowledgeSameMessageWithDifferentStamps()
+    {
+        $envelope1 = new Envelope(new \stdClass(), [new AnEnvelopeStamp()]);
+        $this->transport->send($envelope1);
+        $envelope2 = new Envelope(new \stdClass(), [new AnEnvelopeStamp()]);
+        $this->transport->send($envelope2);
+        $this->assertSame([$envelope1, $envelope2], $this->transport->get());
+        $this->transport->ack($envelope1->with(new AnEnvelopeStamp()));
+        $this->assertSame([$envelope2], $this->transport->get());
+        $this->transport->reject($envelope2->with(new AnEnvelopeStamp()));
+        $this->assertSame([], $this->transport->get());
+    }
+
     public function testAck()
     {
         $envelope = new Envelope(new \stdClass());
diff --git a/src/Symfony/Component/Messenger/Transport/InMemoryTransport.php b/src/Symfony/Component/Messenger/Transport/InMemoryTransport.php
index 354bb601a1..09cbb31a04 100644
--- a/src/Symfony/Component/Messenger/Transport/InMemoryTransport.php
+++ b/src/Symfony/Component/Messenger/Transport/InMemoryTransport.php
@@ -55,7 +55,7 @@ class InMemoryTransport implements TransportInterface, ResetInterface
     public function ack(Envelope $envelope): void
     {
         $this->acknowledged[] = $envelope;
-        $id = spl_object_hash($envelope);
+        $id = spl_object_hash($envelope->getMessage());
         unset($this->queue[$id]);
     }
 
@@ -65,7 +65,7 @@ class InMemoryTransport implements TransportInterface, ResetInterface
     public function reject(Envelope $envelope): void
     {
         $this->rejected[] = $envelope;
-        $id = spl_object_hash($envelope);
+        $id = spl_object_hash($envelope->getMessage());
         unset($this->queue[$id]);
     }
 
@@ -75,7 +75,7 @@ class InMemoryTransport implements TransportInterface, ResetInterface
     public function send(Envelope $envelope): Envelope
     {
         $this->sent[] = $envelope;
-        $id = spl_object_hash($envelope);
+        $id = spl_object_hash($envelope->getMessage());
         $this->queue[$id] = $envelope;
 
         return $envelope;