diff --git a/hgext/mq.py b/hgext/mq.py
--- a/hgext/mq.py
+++ b/hgext/mq.py
@@ -396,12 +396,14 @@
                 self.comments.append('')
             self.comments.append(message)
 
-    def __str__(self):
+    def __bytes__(self):
         s = '\n'.join(self.comments).rstrip()
         if not s:
             return ''
         return s + '\n\n'
 
+    __str__ = encoding.strmethod(__bytes__)
+
     def _delmsg(self):
         '''Remove existing message, keeping the rest of the comments fields.
         If comments contains 'subject: ', message will prepend