diff --git a/addons/point_of_sale/models/pos_config.py b/addons/point_of_sale/models/pos_config.py
index ab1ef162bdd..a62c8334ff0 100644
--- a/addons/point_of_sale/models/pos_config.py
+++ b/addons/point_of_sale/models/pos_config.py
@@ -403,14 +403,15 @@ class PosConfig(models.Model):
         return pos_config
 
     def write(self, vals):
+        opened_session = self.mapped('session_ids').filtered(lambda s: s.state != 'closed')
+        if opened_session:
+            raise UserError(_('Unable to modify this PoS Configuration because there is an open PoS Session based on it.'))
         result = super(PosConfig, self).write(vals)
 
         config_display = self.filtered(lambda c: c.is_posbox and c.iface_customer_facing_display and not (c.customer_facing_display_html or '').strip())
         if config_display:
             super(PosConfig, config_display).write({'customer_facing_display_html': self._compute_default_customer_html()})
 
-        if self.current_session_id:
-            raise UserError(_('Unable to modify this PoS Configuration because there is an open PoS Session based on it.'))
 
         self.sudo()._set_fiscal_position()
         self.sudo()._check_modules_to_install()