diff --git a/setup.py b/setup.py
index 5497b8f..8d39207 100755
--- a/setup.py
+++ b/setup.py
@@ -10,6 +10,7 @@ install_requires = [
     # core dependencies
     'decorator',
     'requests >= 1.0.0',
+    'future',
     'paste',
     'zope.interface',
     'repoze.who',
diff --git a/src/saml2/sigver.py b/src/saml2/sigver.py
index 5ffd21d..60b0deb 100644
--- a/src/saml2/sigver.py
+++ b/src/saml2/sigver.py
@@ -12,11 +12,12 @@ import hashlib
 import logging
 import os
 import ssl
+import six
 
 from time import mktime
 from binascii import hexlify
+
 from future.backports.urllib.parse import urlencode
-import six
 
 # from Crypto.PublicKey.RSA import importKey
 # from Crypto.Signature import PKCS1_v1_5