[racket] Quack in Emacs 24

Has anyone using Quack with Emacs 24 found what the fix is for the 
problem that most of the usual syntax coloring doesn't happen?  (The 
parentheses aren't red, for example.)

When this problem occurs, there will be the following message in the 
"*Messages*" buffer:

     Quack Warning: `font-lock-keywords' already set when hook ran.

I'm still using Emacs 23 (what's in Debian Stable), but I received a bug 
report about Emacs 24 from a user.  I don't immediately have time to 
track down what changed with font-lock or themes (the naive fix I tried 
didn't work), and I don't see a fix in Google.  I was hoping that Emacs 
wouldn't break Quack until I finished Meow. :)  If someone has a simple 
fix, I can add it to the official Quack release, however.

Neil V.