diff --git a/Lib/urllib2.py b/Lib/urllib2.py
index 007e905..09d7f9c 100644
--- a/Lib/urllib2.py
+++ b/Lib/urllib2.py
@@ -948,7 +948,7 @@
             respdig = KD(H(A1), "%s:%s" % (nonce, H(A2)))
         else:
             # XXX handle auth-int.
-            pass
+            raise URLError("qop '%s' is not supported." % qop)
 
         # XXX should the partial digests be encoded too?