--- a/urllib2_kerberos.py
+++ b/urllib2_kerberos.py
@@ -34,6 +34,7 @@ class AbstractKerberosAuthHandler:
         """checks for "Negotiate" in proper auth header
         """
         authreqs = headers.getheaders(self.auth_header)
+        log.debug('authreqs = {}'.format(authreqs))

         if authreqs:

@@ -126,7 +127,8 @@ class AbstractKerberosAuthHandler:
             req.add_unredirected_header(self.authz_header, neg_hdr)
             resp = self.parent.open(req)

-            self.authenticate_server(resp.info())
+            if resp.getcode() != 200:
+                self.authenticate_server(resp.info())

             return resp