diff --git a/edocument.py b/edocument.py
index c71c002..26f2a9d 100644
--- a/edocument.py
+++ b/edocument.py
@@ -63,7 +63,8 @@ class Invoice(Invoice):
                 numtax=len(line.invoice_taxes)))
 
         allowed_cat = ['AE', 'L', 'M', 'E', 'S', 'Z', 'G', 'O', 'K', 'B']
-        if not line.invoice_taxes[0].tax.unece_category_code in allowed_cat:
+        unece_category_code = self.get_category_code(line.invoice_taxes[0].tax)
+        if unece_category_code not in allowed_cat:
             raise UserError(gettext(
                 'edocument_xrechnung.msg_linetax_invalid_catcode',
                 taxname=line.invoice_taxes[0].tax.rec_name,
@@ -99,14 +100,22 @@ class Invoice(Invoice):
                 uomname=line.unit.rec_name))
         return line.unit.unece_code
 
+    def get_category_code(self, tax):
+        while tax:
+            if tax.unece_category_code:
+                return tax.unece_category_code
+                break
+            tax = tax.parent
+
     def tax_category_code(self, tax):
         """ read tax-category, fire exception if missing
         """
-        if len(tax.unece_category_code or '') == 0:
+        unece_category_code = self.get_category_code(tax)
+        if not unece_category_code:
             raise UserError(gettext(
                 'edocument_xrechnung.mds_tax_category_missing',
                 taxname=tax.rec_name))
-        return tax.unece_category_code
+        return unece_category_code
 
     def quote_text(self, text):
         """ replace critical chars