diff --git a/addons/purchase/models/purchase.py b/addons/purchase/models/purchase.py
index d0bdbc3362d..18bf55b5801 100644
--- a/addons/purchase/models/purchase.py
+++ b/addons/purchase/models/purchase.py
@@ -25,6 +25,7 @@ class PurchaseOrder(models.Model):
         for order in self:
             amount_untaxed = amount_tax = 0.0
             for line in order.order_line:
+                line._compute_amount()
                 amount_untaxed += line.price_subtotal
                 amount_tax += line.price_tax
             order.update({