diff --git a/source/app/controllers/util.py b/source/app/controllers/util.py
index 6564405..d3d8a4b 100644
--- a/source/app/controllers/util.py
+++ b/source/app/controllers/util.py
@@ -975,7 +975,10 @@ def _comprobante(doc, options):
     data = CaseInsensitiveDict(doc.attrib.copy())
     del data['certificado']
 
-    data['seriefolio'] = '{} - {}'.format(data['serie'], data['folio'])
+    serie = ''
+    if 'serie' in data:
+        serie = '{} -'.format(data['serie'])
+    data['seriefolio'] = '{}{}'.format(serie, data['folio'])
     data['totalenletras'] = to_letters(float(data['total']), data['moneda'])
     if data['version'] == '3.3':
         tipos = {