diff --git a/novaclient/base.py b/novaclient/base.py
index 5d4b583e4..63cef4e43 100644
--- a/novaclient/base.py
+++ b/novaclient/base.py
@@ -97,7 +97,8 @@ class Manager(utils.HookableMixin):
         # pair
         username = utils.env('OS_USERNAME', 'NOVA_USERNAME')
         url = utils.env('OS_URL', 'NOVA_URL')
-        uniqifier = hashlib.md5(username + url).hexdigest()
+        uniqifier = hashlib.md5(username.encode('utf-8') +
+                                url.encode('utf-8')).hexdigest()
 
         cache_dir = os.path.expanduser(os.path.join(base_dir, uniqifier))