diff --git a/src/Symfony/Component/Messenger/Tests/Transport/Serialization/PhpSerializerTest.php b/src/Symfony/Component/Messenger/Tests/Transport/Serialization/PhpSerializerTest.php
index 53905a053d1a5..1574c5b230415 100644
--- a/src/Symfony/Component/Messenger/Tests/Transport/Serialization/PhpSerializerTest.php
+++ b/src/Symfony/Component/Messenger/Tests/Transport/Serialization/PhpSerializerTest.php
@@ -46,7 +46,7 @@ public function testDecodingFailsWithBadFormat()
         $serializer = new PhpSerializer();
 
         $serializer->decode([
-            'body' => '{"message": "bar"}',
+            'body' => '{"data": "not-serialized"}',
         ]);
     }
 
@@ -58,7 +58,7 @@ public function testDecodingFailsWithBadClass()
         $serializer = new PhpSerializer();
 
         $serializer->decode([
-            'body' => base64_encode('O:13:"ReceivedSt0mp":0:{}'),
+            'body' => json_encode(['data' => 'O:13:"ReceivedSt0mp":0:{}']),
         ]);
     }
 }
diff --git a/src/Symfony/Component/Messenger/Transport/Serialization/PhpSerializer.php b/src/Symfony/Component/Messenger/Transport/Serialization/PhpSerializer.php
index 6a27529c5592d..145927af8af9c 100644
--- a/src/Symfony/Component/Messenger/Transport/Serialization/PhpSerializer.php
+++ b/src/Symfony/Component/Messenger/Transport/Serialization/PhpSerializer.php
@@ -30,13 +30,16 @@ public function decode(array $encodedEnvelope): Envelope
             throw new MessageDecodingFailedException('Encoded envelope should have at least a "body".');
         }
 
-        $serializeEnvelope = base64_decode($encodedEnvelope['body']);
+        $decodedData = \json_decode($encodedEnvelope['body'], true);
+        if (false === $decodedData) {
+            throw new MessageDecodingFailedException('The "body" key could not be JSON decoded.');
+        }
 
-        if (false === $serializeEnvelope) {
-            throw new MessageDecodingFailedException('The "body" key could not be base64 decoded.');
+        if (!isset($decodedData['data'])) {
+            throw new MessageDecodingFailedException('Missing the "data" key on the JSON decoded data..');
         }
 
-        return $this->safelyUnserialize($serializeEnvelope);
+        return $this->safelyUnserialize($decodedData['data']);
     }
 
     /**
@@ -45,7 +48,7 @@ public function decode(array $encodedEnvelope): Envelope
     public function encode(Envelope $envelope): array
     {
         return [
-            'body' => base64_encode(serialize($envelope)),
+            'body' => json_encode(['data' => serialize($envelope)]),
         ];
     }