diff --git a/addons/mail/models/mail_activity.py b/addons/mail/models/mail_activity.py
index a1eb827db98..4f760baad73 100644
--- a/addons/mail/models/mail_activity.py
+++ b/addons/mail/models/mail_activity.py
@@ -602,10 +602,14 @@ class MailActivityMixin(models.AbstractModel):
             activities |= self.env['mail.activity'].create(create_vals)
         return activities
 
-    def activity_reschedule(self, act_type_xmlids, user_id=None, date_deadline=None):
+    def activity_reschedule(self, act_type_xmlids, user_id=None, date_deadline=None, new_user_id=None):
         """ Reschedule some automated activities. Activities to reschedule are
         selected based on type xml ids and optionally by user. Purpose is to be
-        able to change the deadline, not anything else currently. """
+        able to
+
+         * update the deadline to date_deadline;
+         * update the responsible to new_user_id;
+        """
         if self.env.context.get('mail_activity_automation_skip'):
             return False
 
@@ -622,9 +626,12 @@ class MailActivityMixin(models.AbstractModel):
             domain = ['&'] + domain + [('user_id', '=', user_id)]
         activities = self.env['mail.activity'].search(domain)
         if activities:
-            activities.write({
-                'date_deadline': date_deadline,
-            })
+            write_vals = {}
+            if date_deadline:
+                write_vals['date_deadline'] = date_deadline
+            if new_user_id:
+                write_vals['user_id'] = new_user_id
+            activities.write(write_vals)
         return activities
 
     def activity_feedback(self, act_type_xmlids, user_id=None, feedback=None):
diff --git a/addons/test_mail/tests/test_mail_activity.py b/addons/test_mail/tests/test_mail_activity.py
index 7ac2fb5fe95..b29fa7a465b 100644
--- a/addons/test_mail/tests/test_mail_activity.py
+++ b/addons/test_mail/tests/test_mail_activity.py
@@ -157,6 +157,26 @@ class TestMailActivity(BaseFunctionalTest):
         self.assertEqual(rec.active, True)
         self.assertEqual(rec.activity_ids, self.env['mail.activity'])
 
+    def test_activity_mixin_reschedule_user(self):
+        rec = self.test_record.sudo(self.user_employee)
+        rec.activity_schedule(
+            'test_mail.mail_act_test_todo',
+            user_id=self.user_admin.id)
+        self.assertEqual(rec.activity_ids[0].user_id, self.user_admin)
+
+        # reschedule its own should not alter other's activities
+        rec.activity_reschedule(
+            ['test_mail.mail_act_test_todo'],
+            user_id=self.user_employee.id,
+            new_user_id=self.user_employee.id)
+        self.assertEqual(rec.activity_ids[0].user_id, self.user_admin)
+
+        rec.activity_reschedule(
+            ['test_mail.mail_act_test_todo'],
+            user_id=self.user_admin.id,
+            new_user_id=self.user_employee.id)
+        self.assertEqual(rec.activity_ids[0].user_id, self.user_employee)
+
     def test_activity_notify_other_user(self):
         self.user_admin.notification_type = 'email'
         rec = self.test_record.sudo(self.user_employee)