diff --git a/oauth2_provider/oauth2_backends.py b/oauth2_provider/oauth2_backends.py
index 2c5fe1cb5..b7a318c93 100644
--- a/oauth2_provider/oauth2_backends.py
+++ b/oauth2_provider/oauth2_backends.py
@@ -26,7 +26,7 @@ def _get_escaped_full_path(self, request):
         parsed = list(urlparse(request.get_full_path()))
         unsafe = set(c for c in parsed[4]).difference(urlencoded)
         for c in unsafe:
-            parsed[4] = parsed[4].replace(c, quote(c, safe=''))
+            parsed[4] = parsed[4].replace(c, quote(c, safe=b''))
 
         return urlunparse(parsed)