Typeable<n> classes

Hi, I've been trying to use `deriving (Typeable, Data)' on some datatypes with arity 8 and 15, but GHC has been complaining. There aren't any Typeable<n> classes defined in Data.Typeable that go beyond 7. Is there a reason for this particular limit? If not, could it be extended further e.g. to 15? Is this likely to let GHC derive Typeable instances for my data types? Thanks, Matthew