diff --git a/zerver/lib/avatar.py b/zerver/lib/avatar.py
index cbef98df65..feede83885 100644
--- a/zerver/lib/avatar.py
+++ b/zerver/lib/avatar.py
@@ -9,7 +9,7 @@ if False:
 from six import text_type
 
 def gravatar_hash(email):
-    # type: (str) -> str
+    # type: (text_type) -> text_type
     """Compute the Gravatar hash for an email address."""
     # Non-ASCII characters aren't permitted by the currently active e-mail
     # RFCs. However, the IETF has published https://tools.ietf.org/html/rfc4952,
@@ -19,7 +19,7 @@ def gravatar_hash(email):
     return make_safe_digest(email.lower(), hashlib.md5)
 
 def user_avatar_hash(email):
-    # type: (str) -> str
+    # type: (text_type) -> text_type
     # Salting the user_key may be overkill, but it prevents us from
     # basically mimicking Gravatar's hashing scheme, which could lead
     # to some abuse scenarios like folks using us as a free Gravatar
@@ -35,17 +35,17 @@ def avatar_url(user_profile):
     )
 
 def get_avatar_url(avatar_source, email):
-    # type: (str, str) -> str
-    if avatar_source == 'U':
+    # type: (text_type, text_type) -> text_type
+    if avatar_source == u'U':
         hash_key = user_avatar_hash(email)
         if settings.LOCAL_UPLOADS_DIR is not None:
             # ?x=x allows templates to append additional parameters with &s
-            return "/user_avatars/%s.png?x=x" % (hash_key)
+            return u"/user_avatars/%s.png?x=x" % (hash_key)
         else:
             bucket = settings.S3_AVATAR_BUCKET
-            return "https://%s.s3.amazonaws.com/%s?x=x" % (bucket, hash_key)
+            return u"https://%s.s3.amazonaws.com/%s?x=x" % (bucket, hash_key)
     elif settings.ENABLE_GRAVATAR:
         hash_key = gravatar_hash(email)
-        return "https://secure.gravatar.com/avatar/%s?d=identicon" % (hash_key,)
+        return u"https://secure.gravatar.com/avatar/%s?d=identicon" % (hash_key,)
     else:
         return settings.DEFAULT_AVATAR_URI+'?x=x'
diff --git a/zerver/lib/upload.py b/zerver/lib/upload.py
index 4b9de8b5ca..7b2e903303 100644
--- a/zerver/lib/upload.py
+++ b/zerver/lib/upload.py
@@ -27,7 +27,7 @@ import os
 import re
 import six
 from PIL import Image, ImageOps
-from six import text_type
+from six import binary_type, text_type
 from six.moves import cStringIO as StringIO
 import random
 import logging
@@ -102,7 +102,7 @@ class ZulipUploadBackend(object):
 ### S3
 
 def get_bucket(conn, bucket_name):
-    # type: (S3Connection, str) -> Bucket
+    # type: (S3Connection, text_type) -> Bucket
     # Calling get_bucket() with validate=True can apparently lead
     # to expensive S3 bills:
     #    http://www.appneta.com/blog/s3-list-get-bucket-default/
@@ -121,7 +121,7 @@ def upload_image_to_s3(
         user_profile,
         contents,
     ):
-    # type: (str, str, str, UserProfile, str) -> None
+    # type: (text_type, text_type, text_type, UserProfile, text_type) -> None
 
     conn = S3Connection(settings.S3_KEY, settings.S3_SECRET_KEY)
     bucket = get_bucket(conn, bucket_name)
@@ -234,7 +234,7 @@ def mkdirs(path):
         os.makedirs(dirname)
 
 def write_local_file(type, path, file_data):
-    # type: (str, str, str) -> None
+    # type: (text_type, text_type, binary_type) -> None
     file_path = os.path.join(settings.LOCAL_UPLOADS_DIR, type, path)
     mkdirs(file_path)
     with open(file_path, 'wb') as f:
diff --git a/zerver/lib/utils.py b/zerver/lib/utils.py
index 8e99ee99ce..a1e201f56f 100644
--- a/zerver/lib/utils.py
+++ b/zerver/lib/utils.py
@@ -11,6 +11,7 @@ from time import sleep
 
 from django.conf import settings
 from six.moves import range
+from zerver.lib.str_utils import force_text
 
 T = TypeVar('T')
 
@@ -85,13 +86,13 @@ def run_in_batches(all_list, batch_size, callback, sleep_time = 0, logger = None
             sleep(sleep_time)
 
 def make_safe_digest(string, hash_func=hashlib.sha1):
-    # type: (text_type, Callable[[binary_type], Any]) -> str
+    # type: (text_type, Callable[[binary_type], Any]) -> text_type
     """
     return a hex digest of `string`.
     """
     # hashlib.sha1, md5, etc. expect bytes, so non-ASCII strings must
     # be encoded.
-    return hash_func(string.encode('utf-8')).hexdigest()
+    return force_text(hash_func(string.encode('utf-8')).hexdigest())
 
 
 def log_statsd_event(name):
diff --git a/zerver/models.py b/zerver/models.py
index f96ba1b0f1..55e1af35a6 100644
--- a/zerver/models.py
+++ b/zerver/models.py
@@ -1312,7 +1312,7 @@ class Huddle(models.Model):
     huddle_hash = models.CharField(max_length=40, db_index=True, unique=True)
 
 def get_huddle_hash(id_list):
-    # type: (List[int]) -> str
+    # type: (List[int]) -> text_type
     id_list = sorted(set(id_list))
     hash_key = ",".join(str(x) for x in id_list)
     return make_safe_digest(hash_key)