diff --git a/puppet/zulip_internal/files/trac/cgi-bin/trac.fcgi b/puppet/zulip_internal/files/trac/cgi-bin/trac.fcgi
index 627f5cdf3a..ad01b1ce40 100644
--- a/puppet/zulip_internal/files/trac/cgi-bin/trac.fcgi
+++ b/puppet/zulip_internal/files/trac/cgi-bin/trac.fcgi
@@ -41,7 +41,7 @@ except Exception, e:
     print e
     print
     import traceback
-    import StringIO
-    tb = StringIO.StringIO()
+    from six.moves import cStringIO as StringIO
+    tb = StringIO()
     traceback.print_exc(file=tb)
     print tb.getvalue()
diff --git a/tools/deprecated/review b/tools/deprecated/review
index 6597522e44..30630af595 100755
--- a/tools/deprecated/review
+++ b/tools/deprecated/review
@@ -42,7 +42,7 @@ import git
 import shlex
 import codecs
 import fcntl
-from StringIO import StringIO
+from six.moves import cStringIO as StringIO
 from email.message import Message
 from email.header import Header
 from shutil import rmtree, copyfile, copytree
diff --git a/tools/travis/py3k b/tools/travis/py3k
index 6a78639b5e..547c5fcb5c 100755
--- a/tools/travis/py3k
+++ b/tools/travis/py3k
@@ -56,6 +56,13 @@ for fixer in $fixers; do
     fi
 done
 
+if git grep -q '\(^\W*import StringIO\|^\W*from StringIO\)'; then
+    echo "ERROR: StringIO imports not compatible with python 2+3:"
+    git grep '\(^\W*import StringIO\|^\W*from StringIO\)'
+    echo "Please use 'from six.moves import cStringIO as StringIO'"
+    failed=1
+fi
+
 echo
 if [ -z "$failed" ]; then
     echo "No issues detected!"
diff --git a/zerver/decorator.py b/zerver/decorator.py
index 37edebc34d..fab81a0236 100644
--- a/zerver/decorator.py
+++ b/zerver/decorator.py
@@ -10,7 +10,7 @@ from zerver.lib.response import json_error, json_unauthorized
 from django.utils.timezone import now
 from django.conf import settings
 import ujson
-from StringIO import StringIO
+from six.moves import cStringIO as StringIO
 from zerver.lib.queue import queue_json_publish
 from zerver.lib.timestamp import datetime_to_timestamp
 from zerver.lib.utils import statsd
diff --git a/zerver/lib/upload.py b/zerver/lib/upload.py
index def4b981b5..b45fb4d402 100644
--- a/zerver/lib/upload.py
+++ b/zerver/lib/upload.py
@@ -14,7 +14,7 @@ from zerver.models import get_user_profile_by_id
 import base64
 import os
 from PIL import Image, ImageOps
-from StringIO import StringIO
+from six.moves import cStringIO as StringIO
 import random
 
 # Performance Note:
diff --git a/zerver/test_external.py b/zerver/test_external.py
index 9b991af026..bc9d9bfb30 100644
--- a/zerver/test_external.py
+++ b/zerver/test_external.py
@@ -24,7 +24,7 @@ from six.moves import urllib
 
 from boto.s3.connection import S3Connection
 from boto.s3.key import Key
-from StringIO import StringIO
+from six.moves import StringIO
 from six.moves import range
 
 class MITNameTest(TestCase):
diff --git a/zerver/worker/queue_processors.py b/zerver/worker/queue_processors.py
index f9ca5bf69c..3f077084f9 100644
--- a/zerver/worker/queue_processors.py
+++ b/zerver/worker/queue_processors.py
@@ -32,7 +32,7 @@ import time
 import datetime
 import logging
 import simplejson
-import StringIO
+from six.moves import cStringIO as StringIO
 
 def assign_queue(queue_name, enabled=True):
     def decorate(clazz):
@@ -283,7 +283,7 @@ class MessageSenderWorker(QueueProcessingWorker):
                    'SERVER_PORT': 9993,
                    'SERVER_PROTOCOL': 'ZULIP_SOCKET/1.0',
                    'wsgi.version': (1, 0),
-                   'wsgi.input': StringIO.StringIO(),
+                   'wsgi.input': StringIO(),
                    'wsgi.errors': sys.stderr,
                    'wsgi.multithread': False,
                    'wsgi.multiprocess': True,