diff --git a/Lib/urllib2.py b/Lib/urllib2.py
index 09d7f9c..3578e7a 100644
--- a/Lib/urllib2.py
+++ b/Lib/urllib2.py
@@ -298,6 +298,10 @@
         self.process_request = {}
 
     def add_handler(self, handler):
+        if not hasattr(handler, "add_parent"):
+            raise TypeError("expected BaseHandler instance, got %r" %
+                            type(handler))
+
         added = False
         for meth in dir(handler):
             if meth in ["redirect_request", "do_open", "proxy_open"]: