diff --git a/tax.py b/tax.py
--- a/tryton/modules/account/tax.py	Thu Gen 20 10:25:13 2020 +0200
+++ b/tryton/modules/account/tax.py	Thu Gen 20 10:32:48 2020 +0200
@@ -906,7 +906,8 @@ class Tax(sequence_ordered(), ModelSQL, ModelView, DeactivableMixin):
                 if len(tax.childs):
                     values.extend(
                         cls._unit_compute(tax.childs, price_unit, date))
-                if tax.update_unit_price:
+                if (tax.update_unit_price or
+                        tax.parent and tax.parent.update_unit_price):
                     for value in values:
                         unit_price_variation += value['amount']
                 res.extend(values)