diff --git a/purchase_order_uninvoiced_amount/models/purchase_order.py b/purchase_order_uninvoiced_amount/models/purchase_order.py
index ec50615431b..e3b347bc823 100644
--- a/purchase_order_uninvoiced_amount/models/purchase_order.py
+++ b/purchase_order_uninvoiced_amount/models/purchase_order.py
@@ -1,4 +1,5 @@
 # Copyright 2020 Tecnativa - Manuel Calero
+# Copyright 2020 Tecnativa - Pedro M. Baeza
 # License LGPL-3.0 or later (https://www.gnu.org/licenses/lgpl.html).
 
 from odoo import api, fields, models
@@ -11,10 +12,14 @@ class PurchaseOrder(models.Model):
     def _compute_amount_uninvoiced(self):
         for order in self:
             amount_uninvoiced = order.amount_untaxed
-
-            for line in order.order_line.filtered(lambda x: (x.qty_invoiced != 0)):
-                amount_uninvoiced -= line.qty_invoiced * line.price_unit
-
+            for line in order.order_line.filtered("qty_invoiced"):
+                # we use this way for being compatible with purchase_discount
+                price_unit = (
+                    line.product_qty and
+                    line.price_subtotal / line.product_qty or
+                    line.price_unit
+                )
+                amount_uninvoiced -= line.qty_invoiced * price_unit
             order.update({
                 'amount_uninvoiced': order.currency_id.round(amount_uninvoiced),
             })
diff --git a/purchase_order_uninvoiced_amount/tests/test_purchase_order_uninvoiced_amount.py b/purchase_order_uninvoiced_amount/tests/test_purchase_order_uninvoiced_amount.py
index 35b06e4b443..7ec59941475 100644
--- a/purchase_order_uninvoiced_amount/tests/test_purchase_order_uninvoiced_amount.py
+++ b/purchase_order_uninvoiced_amount/tests/test_purchase_order_uninvoiced_amount.py
@@ -1,4 +1,5 @@
 # Copyright 2020 Tecnativa - Manuel Calero
+# Copyright 2020 Tecnativa - Pedro M. Baeza
 # License LGPL-3.0 or later (https://www.gnu.org/licenses/lgpl.html).
 
 from odoo.tests.common import SavepointCase
@@ -105,3 +106,7 @@ def test_create_purchase_create_and_invoiced_with_all_units(self):
         self._create_invoice_from_purchase(purchase)
         self.assertEquals(purchase.amount_uninvoiced, 0,
                           "The purchase amount uninvoiced must be 0")
+
+    def test_create_purchase_qty_0(self):
+        purchase = self._create_purchase(0, 0)
+        self.assertEquals(purchase.amount_uninvoiced, 0)