diff --git a/Lib/cookielib.py b/Lib/cookielib.py
index 268cc20..7fec858 100644
--- a/Lib/cookielib.py
+++ b/Lib/cookielib.py
@@ -26,7 +26,6 @@
 """
 
 import sys, re, urlparse, copy, time, urllib, logging
-from types import StringTypes
 try:
     import threading as _threading
 except ImportError:
@@ -359,7 +358,7 @@
     [[('Basic', None), ('realm', '"foobar"')]]
 
     """
-    assert type(header_values) not in StringTypes
+    assert not isinstance(header_values, basestring)
     result = []
     for text in header_values:
         orig_text = text