1 files changed, 6 insertions, 0 deletions
diff --git a/libraries/base/Data/Functor/Sum.hs b/libraries/base/Data/Functor/Sum.hs
index f7d6178a2b..cca541fe5e 100644
--- a/libraries/base/Data/Functor/Sum.hs
+++ b/libraries/base/Data/Functor/Sum.hs
@@ -1,7 +1,9 @@
 {-# LANGUAGE DeriveDataTypeable #-}
 {-# LANGUAGE DeriveGeneric #-}
 {-# LANGUAGE PolyKinds #-}
+{-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE Safe #-}
+{-# LANGUAGE StandaloneKindSignatures #-}
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Data.Functor.Sum
@@ -23,11 +25,15 @@ module Data.Functor.Sum (
 
 import Control.Applicative ((<|>))
 import Data.Data (Data)
+import Data.Kind (Type)
 import Data.Functor.Classes
 import GHC.Generics (Generic, Generic1)
 import Text.Read (Read(..), readListDefault, readListPrecDefault)
 
 -- | Lifted sum of functors.
+--
+-- Kind `k` explicitly quantified since 4.15.0.0.
+type Sum :: forall k. (k -> Type) -> (k -> Type) -> (k -> Type)
 data Sum f g a = InL (f a) | InR (g a)
   deriving ( Data     -- ^ @since 4.9.0.0
            , Generic  -- ^ @since 4.9.0.0