--- reply-old.lisp	2010-01-08 17:30:22.000000000 +0530
+++ reply.lisp	2010-12-31 17:53:11.000000000 +0530
@@ -154,5 +154,5 @@
    (setf (slot-value reply 'content-length) new-value))
   (:method :after (new-value (name (eql :content-type)) &optional (reply *reply*))
    "Special case for the `Content-Type' header."
-   (check-type new-value string)
+   (check-type new-value (or null string))
    (setf (slot-value reply 'content-type) new-value)))