ghc 5.04 bug

ghc -c Ghcbug.hs
c:\ghc\ghc-5.04\bin\ghc.exe: panic! (the `impossible' happened, GHC 
version 5.04):
       expectJust tyConDataCons

Please report it as a compiler bug to glasgow-haskell-bugs@xxxxxxxxxxx,
or http://sourceforge.net/projects/ghc/.

Ghcbug.hs:
----------------------
module O where

type O a = Ord a => [a]

f :: O a -> O a
f [] = []
------------------------

Cheers,
-- Thomas