diff --git a/facho/fe/form_xml/utils.py b/facho/fe/form_xml/utils.py
index ab626c2..1b4a04a 100644
--- a/facho/fe/form_xml/utils.py
+++ b/facho/fe/form_xml/utils.py
@@ -9,7 +9,7 @@ def DIANWrite(xml, filename):
 
         
 def DIANWriteSigned(xml, filename, private_key, passphrase, use_cache_policy=False):
-    document = xml.tostring(xml_declaration=True, encoding='UTF-8')
+    document = xml.tostring(xml_declaration=True, encoding='UTF-8').encode('utf-8')
     signer = fe.DianXMLExtensionSigner(private_key, passphrase=passphrase, mockpolicy=use_cache_policy)
     with open(filename, 'w') as f:
         f.write(signer.sign_xml_string(document))