diff --git a/addons/resource/models/res_users.py b/addons/resource/models/res_users.py
index 12290b916ec..282ead9147d 100644
--- a/addons/resource/models/res_users.py
+++ b/addons/resource/models/res_users.py
@@ -12,3 +12,13 @@ class ResUsers(models.Model):
     resource_calendar_id = fields.Many2one(
         'resource.calendar', 'Default Working Hours',
         related='resource_ids.calendar_id', readonly=False)
+
+    def write(self, vals):
+        rslt = super().write(vals)
+
+        # If the timezone of the admin user gets set on their first login, also update the timezone of the default working calendar
+        if (vals.get('tz') and len(self) == 1 and not self.env.user.login_date
+            and self.env.user == self.env.ref('base.user_admin') and self == self.env.user):
+            self.resource_calendar_id.tz = vals['tz']
+
+        return rslt