diff --git a/addons/account/models/account_tax.py b/addons/account/models/account_tax.py
index 7c0df6c991f..5ae7aa5a483 100644
--- a/addons/account/models/account_tax.py
+++ b/addons/account/models/account_tax.py
@@ -420,7 +420,7 @@ class AccountTax(models.Model):
 
         # We first need to find out whether this tax computation is made for a refund
         tax_type = self and self[0].type_tax_use
-        is_refund = is_refund or (tax_type == 'sale' and price_unit < 0) or (tax_type == 'purchase' and price_unit > 0)
+        is_refund = is_refund or (tax_type == 'sale' and price_unit > 0) or (tax_type == 'purchase' and price_unit < 0)
 
         rslt = self.with_context(caba_no_transition_account=True)\
                    .compute_all(price_unit, currency=currency_id, quantity=quantity, product=product_id, partner=partner_id, is_refund=is_refund, include_caba_tags=include_caba_tags)