diff --git a/keystoneclient/middleware/s3_token.py b/keystoneclient/middleware/s3_token.py
index 59dd331b5..546fd6aab 100644
--- a/keystoneclient/middleware/s3_token.py
+++ b/keystoneclient/middleware/s3_token.py
@@ -38,6 +38,7 @@ import urllib
 import webob
 
 import requests
+import six
 
 from keystoneclient.openstack.common import jsonutils
 
@@ -134,11 +135,13 @@ class S3Token(object):
         }
         resp = webob.Response(content_type='text/xml')
         resp.status = error_table[code][0]
-        resp.body = error_table[code][1]
-        resp.body = ('<?xml version="1.0" encoding="UTF-8"?>\r\n'
+        error_msg = ('<?xml version="1.0" encoding="UTF-8"?>\r\n'
                      '<Error>\r\n  <Code>%s</Code>\r\n  '
                      '<Message>%s</Message>\r\n</Error>\r\n' %
                      (code, error_table[code][1]))
+        if six.PY3:
+            error_msg = error_msg.encode()
+        resp.body = error_msg
         return resp
 
     def _json_request(self, creds_json):