diff --git a/lib/message.js b/lib/message.js
index ac6e213..eb05b46 100644
--- a/lib/message.js
+++ b/lib/message.js
@@ -287,7 +287,7 @@ define_outcome({
     fields:[
         {name:'delivery_failed', type:'boolean'},
         {name:'undeliverable_here', type:'boolean'},
-        {name:'message_annotations', type:'map'}
+        {name:'message_annotations', type:'symbolic_map'}
     ]});
 
 module.exports = message;