diff --git a/mail_activity_team/models/mail_activity.py b/mail_activity_team/models/mail_activity.py
index 46dd6de2..1fccf746 100644
--- a/mail_activity_team/models/mail_activity.py
+++ b/mail_activity_team/models/mail_activity.py
@@ -46,14 +46,13 @@ class MailActivity(models.Model):
         if not self.team_id:
             return res
         res['domain']['user_id'] = [('id', 'in', self.team_id.member_ids.ids)]
-        if self.user_id and self.user_id in self.team_id.member_ids:
-            return res
-        if self.team_id.user_id:
-            self.user_id = self.team_id.user_id
-        elif self.env.user in self.team_id.member_ids.ids:
-            self.user_id = self.env.user
-        else:
-            self.user_id = self.env['res.users']
+        if self.user_id not in self.team_id.member_ids:
+            if self.team_id.user_id:
+                self.user_id = self.team_id.user_id
+            elif len(self.team_id.member_ids) == 1:
+                self.user_id = self.team_id.member_ids
+            else:
+                self.user_id = self.env['res.users']
         return res
 
     @api.multi
diff --git a/mail_activity_team/models/mail_activity_team.py b/mail_activity_team/models/mail_activity_team.py
index f97c185b..1e44e0d7 100644
--- a/mail_activity_team/models/mail_activity_team.py
+++ b/mail_activity_team/models/mail_activity_team.py
@@ -46,7 +46,6 @@ class MailActivityTeam(models.Model):
     user_id = fields.Many2one(
         comodel_name='res.users',
         string='Team Leader',
-        domain="[('id', 'in', member_ids)]",
     )
     count_missing_activities = fields.Integer(
         string="Missing Activities",
@@ -59,6 +58,13 @@ class MailActivityTeam(models.Model):
         if self.user_id and self.user_id not in self.member_ids:
             self.user_id = False
 
+    @api.onchange('user_id')
+    def _onchange_user_id(self):
+        if self.user_id and self.user_id not in self.member_ids:
+            members_ids = self.member_ids.ids
+            members_ids.append(self.user_id.id)
+            self.member_ids = [(4, member) for member in members_ids]
+
     def assign_team_to_unassigned_activities(self):
         activity_model = self.env['mail.activity']
         for team in self:
@@ -68,4 +74,5 @@ class MailActivityTeam(models.Model):
             if team.res_model_ids:
                 domain.append(('res_model_id', 'in', team.res_model_ids.ids))
             missing_activities = activity_model.search(domain)
-            missing_activities.write({'team_id': team.id})
+            for missing_activity in missing_activities:
+                missing_activity.write({'team_id': team.id})
diff --git a/mail_activity_team/tests/test_mail_activity_team.py b/mail_activity_team/tests/test_mail_activity_team.py
index 3f7928cb..413e4122 100644
--- a/mail_activity_team/tests/test_mail_activity_team.py
+++ b/mail_activity_team/tests/test_mail_activity_team.py
@@ -100,7 +100,7 @@ class TestMailActivityTeam(TransactionCase):
             self.assertEqual(self.act2.team_id, self.team2)
             self.act2.team_id = self.team1
             self.act2._onchange_team_id()
-            self.assertFalse(self.act2.user_id)
+            self.assertEqual(self.act2.user_id, self.team1.member_ids)
             with self.assertRaises(ValidationError):
                 self.act2.write({
                     'user_id': self.employee2.id,
diff --git a/mail_activity_team/views/mail_activity_team_views.xml b/mail_activity_team/views/mail_activity_team_views.xml
index 72b49a1d..6ecba09a 100644
--- a/mail_activity_team/views/mail_activity_team_views.xml
+++ b/mail_activity_team/views/mail_activity_team_views.xml
@@ -27,7 +27,7 @@
                     <group>
                         <group name="base">
                             <field name="name"/>
-                            <field name="user_id" attrs="{'invisible': [('member_ids', '=', [])]}"/>
+                            <field name="user_id"/>
                         </group>
                         <group name="models">
                             <field name="res_model_ids" widget="many2many_tags"