diff --git a/addons/mail/mail_message.py b/addons/mail/mail_message.py
index aec106f766b..6300ccf2bc5 100644
--- a/addons/mail/mail_message.py
+++ b/addons/mail/mail_message.py
@@ -564,6 +564,7 @@ class mail_message(osv.Model):
                 - uid have write access on the related document if model, res_id, OR
                 - otherwise: raise
             - write: if
+                - author_id == pid, uid is the author, OR
                 - uid has write access on the related document if model, res_id
                 - Otherwise: raise
             - unlink: if
@@ -586,7 +587,7 @@ class mail_message(osv.Model):
                 model_record_ids.setdefault(rmod, dict()).setdefault(rid, set()).add(id)
 
         # Author condition, for read and create (private message) -> could become an ir.rule, but not till we do not have a many2one variable field
-        if operation == 'read':
+        if operation == 'read' or operation == 'write':
             author_ids = [mid for mid, message in message_values.iteritems()
                 if message.get('author_id') and message.get('author_id') == partner_id]
         elif operation == 'create':
diff --git a/addons/mail/wizard/invite.py b/addons/mail/wizard/invite.py
index 6deaf133bf5..6022d2b07be 100644
--- a/addons/mail/wizard/invite.py
+++ b/addons/mail/wizard/invite.py
@@ -71,6 +71,8 @@ class invite_wizard(osv.osv_memory):
             
             # send an email
             if wizard.message:
+                # the invite wizard should create a private message not related to any object,
+                # we ensure that by overwriting off res_id and res_model default value of the context
                 for follower_id in new_follower_ids:
                     mail_mail = self.pool.get('mail.mail')
                     mail_id = mail_mail.create(cr, uid, {