[racket] Units and serializable-struct

I am writing a program using units and got this message:
define-signature: unknown signature form in: serializable-struct

Sure enough, the docs show that serializable-struct is not allowed in a
signature. Is this something that can be fixed or do I have to work around
it (maybe by using regular structs and writing my own read-struct and
write-struct routines)? What is the best course of action?

Justin
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.racket-lang.org/users/archive/attachments/20150204/b16a3727/attachment.html>