diff --git a/src/Message.php b/src/Message.php
index 11ec16330..008e23f36 100644
--- a/src/Message.php
+++ b/src/Message.php
@@ -19,7 +19,7 @@ class Message implements MessageInterface
     protected $metadata = [];
 
     /**
-     * @var string
+     * @var mixed
      */
     protected $content = '';