diff --git a/addons/mail/mail_message.py b/addons/mail/mail_message.py
index c103926bdac..d4ea41fedfe 100644
--- a/addons/mail/mail_message.py
+++ b/addons/mail/mail_message.py
@@ -263,7 +263,7 @@ class mail_message(osv.osv):
             attachment_data = {
                     'name': fname,
                     'datas_fname': fname,
-                    'datas': fcontent,
+                    'datas': fcontent and fcontent.encode('base64'),
                     'res_model': self._name,
                     'res_id': email_msg_id,
             }
diff --git a/addons/mail/wizard/mail_compose_message.py b/addons/mail/wizard/mail_compose_message.py
index e68bd70a739..af8baa314de 100644
--- a/addons/mail/wizard/mail_compose_message.py
+++ b/addons/mail/wizard/mail_compose_message.py
@@ -194,7 +194,7 @@ class mail_compose_message(osv.osv_memory):
         for mail in self.browse(cr, uid, ids, context=context):
             attachment = {}
             for attach in mail.attachment_ids:
-                attachment[attach.datas_fname] = attach.datas
+                attachment[attach.datas_fname] = attach.datas and attach.datas.decode('base64')
             references = None
             headers = {}