diff --git a/setup.py b/setup.py
index 132c4b75..d72a9aaf 100644
--- a/setup.py
+++ b/setup.py
@@ -50,6 +50,7 @@ def read(fname):
         "attrs>=19.1.0",
         "netaddr>=0.7.0",
         "sortedcontainers>=2.1.0",
+        "six>=1.10",
     ],
     # make sure we package the sql files
     include_package_data=True,
diff --git a/sydent/http/servlets/store_invite_servlet.py b/sydent/http/servlets/store_invite_servlet.py
index fbab903f..e5dd7181 100644
--- a/sydent/http/servlets/store_invite_servlet.py
+++ b/sydent/http/servlets/store_invite_servlet.py
@@ -18,6 +18,7 @@
 import string
 from email.header import Header
 
+from six import string_types
 from twisted.web.resource import Resource
 from unpaddedbase64 import encode_base64
 
@@ -75,9 +76,9 @@ def render_POST(self, request):
         tokenStore.storeToken(medium, address, roomId, sender, token)
 
         substitutions = {}
-        for key, values in request.args.items():
-            if len(values) == 1 and type(values[0]) == str:
-                substitutions[key] = values[0]
+        for k, v in args.items():
+            if isinstance(v, string_types):
+                substitutions[k] = v
         substitutions["token"] = token
 
         required = [