diff --git a/utils/he_ipv6/tunnel.py b/utils/he_ipv6/tunnel.py
index 3f47ad4..a48e153 100644
--- a/utils/he_ipv6/tunnel.py
+++ b/utils/he_ipv6/tunnel.py
@@ -137,7 +137,7 @@ class Assignment(object):
             # We need to do some funky things here. Netaddr doesn't have an .exploded().
             _base = ipaddress.IPv6Address(str(i.ip))
             _base = ipaddress.IPv6Address(re.sub(r'(:0000){4}$', r':dead:beef:cafe::', str(_base.exploded)))
-            _base = re.sub(r':0$', r'', _base)
+            _base = re.sub(r':0$', r'', str(_base))
             logger.debug('Base prefix for {0}: {1}'.format(str(i), _base))
             start = '{0}:0'.format(_base)
             stop = '{0}:ffff'.format(_base)