Unparseable code error failing to result in any error message being presented

[SarmBoJim]

When I use this code:
(def ISBN-LENGTH 13)
(def OLD-ISBN-LENGTH 10)
(defn valid-isbn [isbn]
(or (= (count isbn) OLD-ISBN-LENGTH)
(= (count isbn) ISBN-LENGTH)))

And then enter: (valid-isbn 05967)
and submit for evaluation, nothing at all happens, no error message.
It has a leading zero so is invalid code but still should present an error message of some sort I would think.