diff --git a/addons/resource/models/res_users.py b/addons/resource/models/res_users.py
index 1ff3a82227234..ef4f885919e56 100644
--- a/addons/resource/models/res_users.py
+++ b/addons/resource/models/res_users.py
@@ -19,6 +19,9 @@ def write(self, 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', False) and self == self.env.user):
-            self.resource_calendar_id.tz = vals['tz']
+            if self.resource_calendar_id:
+                self.resource_calendar_id.tz = vals['tz']
+            else:
+                self.env.ref('resource.resource_calendar_std', False).tz = vals['tz']
 
         return rslt