diff --git a/lib/py/src/transport/THttpClient.py b/lib/py/src/transport/THttpClient.py
index 82ca3d12dfb..c2a4f14e6de 100644
--- a/lib/py/src/transport/THttpClient.py
+++ b/lib/py/src/transport/THttpClient.py
@@ -100,7 +100,7 @@ def basic_proxy_auth_header(proxy):
         ap = "%s:%s" % (urllib.parse.unquote(proxy.username),
                         urllib.parse.unquote(proxy.password))
         cr = base64.b64encode(ap.encode()).strip()
-        return "Basic " + cr
+        return "Basic " + six.ensure_str(cr)
 
     def using_proxy(self):
         return self.realhost is not None