Generic Haskell is a language extension of Haskell for polytypic programming. Constrained types are parametric algebraic types with at least one argument constrained by type-class membership.We explain Generic Haskell, discuss the relevance of constrained types, and show that they are not supported by Generic Haskell. We propose context-parametric polykinded types as a solution, thereby making polytypic functions generic on a larger class of types. Our proposal entails an extension to the Generic Haskell compiler, not the language, and is therefore transparent to the generic programmer