diff --git a/addons/mail/doc/mail_state.rst b/addons/mail/doc/mail_state.rst
index bd8052656d2..527a31ba835 100644
--- a/addons/mail/doc/mail_state.rst
+++ b/addons/mail/doc/mail_state.rst
@@ -24,5 +24,5 @@ mechanism [REF].
     result = super(ir_needaction_mixin, self).get_needaction_user_ids(cr, uid, ids, context=context)
     for obj in self.browse(cr, uid, ids, context=context):
       if obj.message_state == False and obj.user_id:
-        result[obj.id].add(obj.user_id.id)
+        result[obj.id].append(obj.user_id.id)
     return result
diff --git a/addons/mail/ir_needaction.py b/addons/mail/ir_needaction.py
index ce306050e26..8193ac4f385 100644
--- a/addons/mail/ir_needaction.py
+++ b/addons/mail/ir_needaction.py
@@ -22,15 +22,18 @@
 from osv import osv
 
 class ir_needaction_mixin(osv.Model):
-    """ Update of res.users class
-        - add a preference about sending emails about notificatoins
-        - make a new user follow itself
+    """ Update of ir.needaction_mixin class
+        - override the get_needaction_user_ids method to define the default
+          mail gateway need_action: when the object is unread, the object
+          responsible has an action to perform.
     """
     _name = 'ir.needaction_mixin'
     _inherit = ['ir.needaction_mixin']
     
     def get_needaction_user_ids(self, cr, uid, ids, context=None):
-        """ Returns the user_ids that have to perform an action
+        """ Returns the user_ids that have to perform an action. It the
+            document mail state is unread (False), return object.user_id.id
+            as need_action uid.
             :return: dict { record_id: [user_ids], }
         """
         result = super(ir_needaction_mixin, self).get_needaction_user_ids(cr, uid, ids, context=context)