diff --git a/mixin.py b/mixin.py
index 2879910..e8762fe 100644
--- a/mixin.py
+++ b/mixin.py
@@ -110,8 +110,8 @@ class EdocumentMixin(object):
         tax = line.taxes[0]
         date = line.invoice.accounting_date or line.invoice.invoice_date
         for child in tax.childs:
-            start_date = tax.start_date or datetime.date.min
-            end_date = tax.end_date or datetime.date.max
+            start_date = child.start_date or datetime.date.min
+            end_date = child.end_date or datetime.date.max
             if start_date <= date <= end_date:
                 tax = child
                 break