The Haskell 98 Report says kind inference is to be done over dependency groups with polymorphic kinds defaulted to *, and hence the following example (from 4.6) is illegal: data Tree a = Leaf | Fork (Tree a) (Tree a) type TreeList = Tree [] GHC 6.4 seems to perform kind inference across all the data, newtype, type and class declarations of a module before defaulting, and so accepts the above. An improvement, I think, but unadvertised. Was it intentional?