; (tyvars, theta, tau) <- tcHsInstHead poly_ty
-- Now, check the validity of the instance.
- ; (clas, inst_tys) <- checkValidInstHead tau
- ; checkValidInstance tyvars theta clas inst_tys
+ ; (clas, inst_tys) <- checkValidInstance poly_ty tyvars theta tau
-- Next, process any associated types.
; idx_tycons <- recoverM (return []) $
-- If there are no superclasses, matters are simpler, because we don't need the case
-- see Note [Newtype deriving superclasses] in TcDeriv.lhs
-tc_inst_decl2 dfun_id (NewTypeDerived coi)
+tc_inst_decl2 dfun_id (NewTypeDerived coi _)
= do { let rigid_info = InstSkol
origin = SigOrigin rigid_info
inst_ty = idType dfun_id