diff --git a/addons/website_sale_stock/models/sale_order.py b/addons/website_sale_stock/models/sale_order.py
index 391ad44b4af..169f97cba60 100644
--- a/addons/website_sale_stock/models/sale_order.py
+++ b/addons/website_sale_stock/models/sale_order.py
@@ -17,8 +17,11 @@ class SaleOrder(models.Model):
         for line in self.order_line:
             if line.product_id.type == 'product' and line.product_id.inventory_availability in ['always', 'threshold']:
                 cart_qty = sum(self.order_line.filtered(lambda p: p.product_id.id == line.product_id.id).mapped('product_uom_qty'))
-                if cart_qty > line.product_id.with_context(warehouse=self.warehouse_id.id).virtual_available and (line_id == line.id):
-                    qty = line.product_id.with_context(warehouse=self.warehouse_id.id).virtual_available - cart_qty
+                # The quantity should be computed based on the warehouse of the website, not the
+                # warehouse of the SO.
+                website = self.env['website'].get_current_website()
+                if cart_qty > line.product_id.with_context(warehouse=website.warehouse_id.id).virtual_available and (line_id == line.id):
+                    qty = line.product_id.with_context(warehouse=website.warehouse_id.id).virtual_available - cart_qty
                     new_val = super(SaleOrder, self)._cart_update(line.product_id.id, line.id, qty, 0, **kwargs)
                     values.update(new_val)