diff --git a/addons/mail/mail_thread.py b/addons/mail/mail_thread.py
index ee039533af6b8..e82ed94c43b9d 100644
--- a/addons/mail/mail_thread.py
+++ b/addons/mail/mail_thread.py
@@ -1166,7 +1166,9 @@ def message_post(self, cr, uid, thread_id, body='', subject=None, type='notifica
 
         # _mail_flat_thread: automatically set free messages to the first posted message
         if self._mail_flat_thread and not parent_id and thread_id:
-            message_ids = mail_message.search(cr, uid, ['&', ('res_id', '=', thread_id), ('model', '=', model)], context=context, order="id ASC", limit=1)
+            message_ids = mail_message.search(cr, uid, ['&', ('res_id', '=', thread_id), ('model', '=', model), ('type', '=', 'email')], context=context, order="id ASC", limit=1)
+            if not message_ids:
+                message_ids = message_ids = mail_message.search(cr, uid, ['&', ('res_id', '=', thread_id), ('model', '=', model)], context=context, order="id ASC", limit=1)
             parent_id = message_ids and message_ids[0] or False
         # we want to set a parent: force to set the parent_id to the oldest ancestor, to avoid having more than 1 level of thread
         elif parent_id: