diff --git a/addons/account/models/product.py b/addons/account/models/product.py
index 5de8659a39c..9297ee2cfdd 100644
--- a/addons/account/models/product.py
+++ b/addons/account/models/product.py
@@ -123,7 +123,6 @@ class ProductProduct(models.Model):
     def _get_product_accounts(self):
         return self.product_tmpl_id._get_product_accounts()
 
-    @api.model
     def _get_tax_included_unit_price(self, company, currency, document_date, document_type,
             is_refund_document=False, product_uom=None, product_currency=None,
             product_price_unit=None, product_taxes=None, fiscal_position=None
@@ -131,6 +130,8 @@ class ProductProduct(models.Model):
         """ Helper to get the price unit from different models.
             This is needed to compute the same unit price in different models (sale order, account move, etc.) with same parameters.
         """
+        self.ensure_one()
+        company.ensure_one()
 
         product = self
 
diff --git a/addons/sale/models/sale_order_line.py b/addons/sale/models/sale_order_line.py
index 7769978de8c..e7a6eead58d 100644
--- a/addons/sale/models/sale_order_line.py
+++ b/addons/sale/models/sale_order_line.py
@@ -433,7 +433,7 @@ class SaleOrderLine(models.Model):
             else:
                 price = line.with_company(line.company_id)._get_display_price()
                 line.price_unit = line.product_id._get_tax_included_unit_price(
-                    line.company_id,
+                    line.company_id or line.env.company,
                     line.order_id.currency_id,
                     line.order_id.date_order,
                     'sale',