diff --git a/mail_activity_team/models/mail_activity.py b/mail_activity_team/models/mail_activity.py
index 3f2e9640b5..d0a11e68dc 100644
--- a/mail_activity_team/models/mail_activity.py
+++ b/mail_activity_team/models/mail_activity.py
@@ -27,6 +27,24 @@ def _get_default_team_id(self, user_id=None):
         comodel_name="mail.activity.team", default=lambda s: s._get_default_team_id()
     )
 
+    @api.model_create_multi
+    def create(self, vals_list):
+        vals_list = [
+            # ensure that the built-in user_id field value is in sync with our field
+            # team_user_id before triggering create
+            (
+                dict(vals, user_id=vals["team_user_id"])
+                if (
+                    "user_id" in vals
+                    and "team_user_id" in vals
+                    and vals["user_id"] != vals["team_user_id"]
+                )
+                else vals
+            )
+            for vals in vals_list
+        ]
+        return super(MailActivity, self).create(vals_list)
+
     @api.onchange("user_id")
     def _onchange_user_id(self):
         if not self.user_id or (
@@ -67,7 +85,7 @@ def _check_team_and_user(self):
 
     @api.onchange("activity_type_id")
     def _onchange_activity_type_id(self):
-        super(MailActivity, self)._onchange_activity_type_id()
+        super()._onchange_activity_type_id()
         if self.activity_type_id.default_team_id:
             self.team_id = self.activity_type_id.default_team_id
             members = self.activity_type_id.default_team_id.member_ids
diff --git a/mail_activity_team/tests/test_mail_activity_team.py b/mail_activity_team/tests/test_mail_activity_team.py
index 91fbbff43a..4bc51ae880 100644
--- a/mail_activity_team/tests/test_mail_activity_team.py
+++ b/mail_activity_team/tests/test_mail_activity_team.py
@@ -313,3 +313,35 @@ def test_activity_schedule_next(self):
         self.assertTrue(next_activities)
         self.assertEqual(next_activities.team_id, self.team2)
         self.assertEqual(next_activities.user_id, self.employee2)
+
+    def test_user_sync(self):
+        messages_domain = [
+            ("res_id", "=", self.partner_client.id),
+            ("model", "=", self.partner_ir_model.model),
+        ]
+        messages_ids = self.env["mail.message"].search(messages_domain)
+        self.assertFalse(messages_ids)
+        # create a new activity
+        activity_form = Form(self.env["mail.activity"].with_user(self.employee))
+        # ensure default values are set
+        self.assertEqual(activity_form.team_id, self.team1)
+        self.assertEqual(activity_form.user_id, self.employee)
+        # assign new activity values
+        activity_form.activity_type_id = self.activity2
+        activity_form.res_model_id = self.partner_ir_model
+        activity_form.res_id = self.partner_client
+        # set another user (the `user_id` field is hidden and replaced with
+        # `team_user_id` when this module is installed)
+        activity_form.team_user_id = self.employee2
+        activity_form.team_id = self.team2
+        activity_id = activity_form.save()
+        # check right values
+        self.assertEqual(activity_id.user_id, self.employee2)
+        self.assertEqual(activity_id.team_user_id, self.employee2)
+        self.assertEqual(activity_id.team_id, self.team2)
+        # ensure that one and only one notification has been created
+        messages_id = self.env["mail.message"].search(messages_domain)
+        self.assertEqual(len(messages_id), 1)
+        self.assertEqual(messages_id.email_from, '"Employee" <crmuser@yourcompany.com>')
+        self.assertEqual(messages_id.partner_ids, self.employee2.partner_id)
+        self.assertRegex(messages_id.body, r"Employee.*assigned you an activity")