diff --git a/imagekit/utils.py b/imagekit/utils.py
index 598be43..baaf234 100644
--- a/imagekit/utils.py
+++ b/imagekit/utils.py
@@ -1,14 +1,18 @@
 from __future__ import unicode_literals
 import logging
+import re
 from tempfile import NamedTemporaryFile
+from hashlib import md5
 
 from django.conf import settings
 from django.core.exceptions import ImproperlyConfigured
 from django.core.files import File
 from django.utils.importlib import import_module
-from hashlib import md5
+try:
+    from django.utils.encoding import force_bytes
+except ImportError:
+    from django.utils.encoding import smart_str as force_bytes
 from pilkit.utils import *
-import re
 from .lib import NullHandler
 
 
@@ -148,7 +152,7 @@ def sanitize_cache_key(key):
         # The also can't be > 250 chars long. Since we don't know what the
         # user's cache ``KEY_FUNCTION`` setting is like, we'll limit it to 200.
         if len(new_key) >= 200:
-            new_key = '%s:%s' % (new_key[:200-33], md5(key).hexdigest())
+            new_key = '%s:%s' % (new_key[:200-33], md5(force_bytes(key)).hexdigest())
 
         key = new_key
     return key
diff --git a/tests/test_cachefiles.py b/tests/test_cachefiles.py
index 4338a82..ba250fb 100644
--- a/tests/test_cachefiles.py
+++ b/tests/test_cachefiles.py
@@ -1,4 +1,8 @@
 from django.conf import settings
+try:
+    from django.utils.encoding import force_bytes
+except ImportError:
+    from django.utils.encoding import smart_str as force_bytes
 from hashlib import md5
 from imagekit.cachefiles import ImageCacheFile, LazyImageCacheFile
 from imagekit.cachefiles.backends import Simple
@@ -73,7 +77,7 @@ def test_memcached_cache_key():
     eq_(backend.get_key(file), '%s%s:%s' % (
         settings.IMAGEKIT_CACHE_PREFIX,
         '1' * (200 - len(':') - 32 - len(settings.IMAGEKIT_CACHE_PREFIX)),
-        md5('%s%s-state' % (settings.IMAGEKIT_CACHE_PREFIX, filename)).hexdigest()))
+        md5(force_bytes('%s%s-state' % (settings.IMAGEKIT_CACHE_PREFIX, filename))).hexdigest()))
 
 
 def test_lazyfile_stringification():