--- a/bert/codec.py	2018-03-07 20:11:38.117925147 -0800
+++ b/bert/codec.py	2018-03-07 20:12:19.681258078 -0800
@@ -92,7 +92,7 @@
             return (Atom("bert"), Atom("false"))
         elif obj is None:
             return (Atom("bert"), Atom("nil"))
-        elif isinstance(obj, basestring) and not self.__is_ascii(obj):
+        elif isinstance(obj, str) and not self.__is_ascii(obj):
             return (Atom("bert"), Atom("string"), Atom(self.encoding.upper()), obj.encode(self.encoding))
         elif isinstance(obj, dict):
             return (Atom("bert"), Atom("dict"), [(self.convert(k), self.convert(v)) for k, v in obj.items()])