diff --git a/addons/website_sale_stock/i18n/website_sale_stock.pot b/addons/website_sale_stock/i18n/website_sale_stock.pot
index b4918377c23..1a2410a8298 100644
--- a/addons/website_sale_stock/i18n/website_sale_stock.pot
+++ b/addons/website_sale_stock/i18n/website_sale_stock.pot
@@ -189,6 +189,13 @@ msgstr ""
 msgid "The following product is now available."
 msgstr ""
 
+#. module: website_sale_stock
+#. odoo-python
+#: code:addons/website_sale_stock/models/sale_order.py:0
+#, python-format
+msgid "The item has not been added to your cart since it is not available."
+msgstr ""
+
 #. module: website_sale_stock
 #. odoo-python
 #: code:addons/website_sale_stock/models/product_product.py:0
diff --git a/addons/website_sale_stock/models/sale_order.py b/addons/website_sale_stock/models/sale_order.py
index 386fd599109..373433291ec 100644
--- a/addons/website_sale_stock/models/sale_order.py
+++ b/addons/website_sale_stock/models/sale_order.py
@@ -41,12 +41,21 @@ class SaleOrder(models.Model):
                         order_line._set_shop_warning_stock(total_cart_qty, available_qty)
                     else:
                         self._set_shop_warning_stock(total_cart_qty, available_qty)
+                    returned_warning = order_line.shop_warning or self.shop_warning
                 else:  # 0 or negative allowed_qty
                     # if existing line: it will be deleted
                     # if no existing line: no line will be created
-                    self.shop_warning = _(
-                        "Some products became unavailable and your cart has been updated. We're sorry for the inconvenience.")
-                return allowed_line_qty, order_line.shop_warning or self.shop_warning
+                    if order_line:
+                        self.shop_warning = _(
+                            "Some products became unavailable and your cart has been updated. We're"
+                            " sorry for the inconvenience."
+                        )
+                        returned_warning = self.shop_warning
+                    else:
+                        returned_warning = _(
+                            "The item has not been added to your cart since it is not available."
+                        )
+                return allowed_line_qty, returned_warning
         return super()._verify_updated_quantity(order_line, product_id, new_qty, **kwargs)
 
     def _get_cart_and_free_qty(self, product, line=None):