-- 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