diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,3 +1,8 @@
+# 1.0.3
+
+- Make `GNFData` PolyKinded.
+- Add `GNFData ((:~:) a)` and `GNFData TypeRep` instances
+
 # 1.0.2
 
 - Explicitly mark `Data.Some` as `Safe`.
diff --git a/some.cabal b/some.cabal
--- a/some.cabal
+++ b/some.cabal
@@ -1,5 +1,5 @@
 name:               some
-version:            1.0.2
+version:            1.0.3
 stability:          provisional
 cabal-version:      >=1.10
 build-type:         Simple
@@ -36,7 +36,8 @@
    || ==8.4.4
    || ==8.6.5
    || ==8.8.4
-   || ==8.10.3
+   || ==8.10.4
+   || ==9.0.1
 
 extra-source-files: ChangeLog.md
 
@@ -59,11 +60,12 @@
   if flag(newtype-unsafe)
     cpp-options: -DSOME_NEWTYPE
 
+  -- main module
+  exposed-modules:  Data.Some
   exposed-modules:
     Data.GADT.Compare
     Data.GADT.DeepSeq
     Data.GADT.Show
-    Data.Some
     Data.Some.Church
     Data.Some.GADT
     Data.Some.Newtype
@@ -82,10 +84,13 @@
       , transformers         >=0.3    && <0.6
       , transformers-compat  >=0.6    && <0.7
 
-  if impl(ghc >= 9.0)
+  if impl(ghc >=9.0)
     -- these flags may abort compilation with GHC-8.10
     -- https://gitlab.haskell.org/ghc/ghc/-/merge_requests/3295
     ghc-options: -Winferred-safe-imports -Wmissing-safe-haskell-mode
+
+  if impl(ghc >=9.1)
+    ghc-options: -Wmissing-kind-signatures
 
 test-suite hkd-example
   default-language: Haskell2010
diff --git a/src/Data/GADT/DeepSeq.hs b/src/Data/GADT/DeepSeq.hs
--- a/src/Data/GADT/DeepSeq.hs
+++ b/src/Data/GADT/DeepSeq.hs
@@ -1,5 +1,12 @@
 {-# LANGUAGE CPP         #-}
-#if __GLASGOW_HASKELL__ >= 704
+{-# LANGUAGE GADTs       #-}
+#if __GLASGOW_HASKELL__ >= 706
+{-# LANGUAGE PolyKinds   #-}
+#endif
+#if __GLASGOW_HASKELL__ >= 810
+{-# LANGUAGE StandaloneKindSignatures #-}
+#endif
+#if (__GLASGOW_HASKELL__ >= 704 && __GLASGOW_HASKELL__ < 707) || __GLASGOW_HASKELL__ >= 801
 {-# LANGUAGE Safe        #-}
 #elif __GLASGOW_HASKELL__ >= 702
 {-# LANGUAGE Trustworthy #-}
@@ -10,7 +17,20 @@
 
 import Data.Functor.Product (Product (..))
 import Data.Functor.Sum     (Sum (..))
+import Data.Type.Equality   ((:~:) (..))
 
+#if MIN_VERSION_base(4,10,0)
+import qualified Type.Reflection    as TR
+#endif
+
+#if __GLASGOW_HASKELL__ >= 810
+import Data.Kind (Type, Constraint)
+#endif
+
+#if __GLASGOW_HASKELL__ >= 810
+type GNFData :: (k -> Type) -> Constraint
+#endif
+
 class GNFData f where
     grnf :: f a -> ()
 
@@ -20,3 +40,13 @@
 instance (GNFData a, GNFData b) => GNFData (Sum a b) where
     grnf (InL x) = grnf x
     grnf (InR y) = grnf y
+
+-- | @since 1.0.3
+instance GNFData ((:~:) a) where
+    grnf Refl = ()
+
+#if MIN_VERSION_base(4,10,0)
+-- | @since 1.0.3
+instance GNFData TR.TypeRep where
+    grnf = TR.rnfTypeRep
+#endif
diff --git a/src/Data/GADT/Internal.hs b/src/Data/GADT/Internal.hs
--- a/src/Data/GADT/Internal.hs
+++ b/src/Data/GADT/Internal.hs
@@ -7,15 +7,17 @@
 #if __GLASGOW_HASKELL__ >= 706
 {-# LANGUAGE PolyKinds           #-}
 #endif
-#if __GLASGOW_HASKELL__ >= 704
-#define GHC __GLASGOW_HASKELL__
-#if (GHC >= 704 && GHC <707) || GHC >= 801
+#if __GLASGOW_HASKELL__ >= 708
+{-# LANGUAGE RoleAnnotations #-}
+#endif
+#if __GLASGOW_HASKELL__ >= 810
+{-# LANGUAGE StandaloneKindSignatures #-}
+#endif
+#if (__GLASGOW_HASKELL__ >= 704 && __GLASGOW_HASKELL__ < 707) || __GLASGOW_HASKELL__ >= 801
 {-# LANGUAGE Safe                #-}
-#else
+#elif __GLASGOW_HASKELL__ >= 702
 {-# LANGUAGE Trustworthy         #-}
 #endif
-#undef GHC
-#endif
 module Data.GADT.Internal where
 
 import Control.Applicative  (Applicative (..))
@@ -35,6 +37,10 @@
 import qualified Type.Reflection    as TR
 #endif
 
+#if __GLASGOW_HASKELL__ >= 810
+import Data.Kind (Type, Constraint)
+#endif
+
 -- $setup
 -- >>> :set -XKindSignatures -XGADTs
 
@@ -43,6 +49,9 @@
 -- to write (or derive) an @instance Show (T a)@, and then simply say:
 --
 -- > instance GShow t where gshowsPrec = showsPrec
+#if __GLASGOW_HASKELL__ >= 810
+type GShow :: (k -> Type) -> Constraint
+#endif
 class GShow t where
     gshowsPrec :: Int -> t a -> ShowS
 
@@ -79,6 +88,9 @@
 
 -- |@GReadS t@ is equivalent to @ReadS (forall b. (forall a. t a -> b) -> b)@, which is
 -- in turn equivalent to @ReadS (Exists t)@ (with @data Exists t where Exists :: t a -> Exists t@)
+#if __GLASGOW_HASKELL__ >= 810
+type GReadS :: (k -> Type) -> Type
+#endif
 type GReadS t = String -> [(Some t, String)]
 
 getGReadResult :: Some tag -> (forall a. tag a -> b) -> b
@@ -90,6 +102,9 @@
 -- |'Read'-like class for 1-type-parameter GADTs.  Unlike 'GShow', this one cannot be
 -- mechanically derived from a 'Read' instance because 'greadsPrec' must choose the phantom
 -- type based on the 'String' being parsed.
+#if __GLASGOW_HASKELL__ >= 810
+type GRead :: (k -> Type) -> Constraint
+#endif
 class GRead t where
     greadsPrec :: Int -> GReadS t
 
@@ -139,6 +154,9 @@
 -- |A class for type-contexts which contain enough information
 -- to (at least in some cases) decide the equality of types
 -- occurring within them.
+#if __GLASGOW_HASKELL__ >= 810
+type GEq :: (k -> Type) -> Constraint
+#endif
 class GEq f where
     -- |Produce a witness of type-equality, if one exists.
     --
@@ -219,6 +237,9 @@
 -- |A type for the result of comparing GADT constructors; the type parameters
 -- of the GADT values being compared are included so that in the case where
 -- they are equal their parameter types can be unified.
+#if __GLASGOW_HASKELL__ >= 810
+type GOrdering :: k -> k -> Type
+#endif
 data GOrdering a b where
     GLT :: GOrdering a b
     GEQ :: GOrdering t t
@@ -259,6 +280,9 @@
 
 -- |Type class for comparable GADT-like structures.  When 2 things are equal,
 -- must return a witness that their parameter types are equal as well ('GEQ').
+#if __GLASGOW_HASKELL__ >= 810
+type GCompare :: (k -> Type) -> Constraint
+#endif
 class GEq f => GCompare f where
     gcompare :: f a -> f b -> GOrdering a b
 
@@ -343,10 +367,17 @@
 -- >>> read "mkSome TagInt" :: Some Tag
 -- mkSome TagInt
 --
+#if __GLASGOW_HASKELL__ >= 810
+type Some :: (k -> Type) -> Type
+#endif
 newtype Some tag = S
     { -- | Eliminator.
       withSome :: forall r. (forall a. tag a -> r) -> r
     }
+
+#if __GLASGOW_HASKELL__ >= 708
+type role Some representational
+#endif
 
 -- | Constructor.
 mkSome :: tag a -> Some tag
diff --git a/src/Data/Some/GADT.hs b/src/Data/Some/GADT.hs
--- a/src/Data/Some/GADT.hs
+++ b/src/Data/Some/GADT.hs
@@ -4,6 +4,12 @@
 #if __GLASGOW_HASKELL__ >= 706
 {-# LANGUAGE PolyKinds   #-}
 #endif
+#if __GLASGOW_HASKELL__ >= 708
+{-# LANGUAGE RoleAnnotations #-}
+#endif
+#if __GLASGOW_HASKELL__ >= 810
+{-# LANGUAGE StandaloneKindSignatures #-}
+#endif
 #if __GLASGOW_HASKELL__ >= 704
 {-# LANGUAGE Safe        #-}
 #elif __GLASGOW_HASKELL__ >= 702
@@ -24,10 +30,15 @@
 import Data.Monoid         (Monoid (..))
 import Data.Semigroup      (Semigroup (..))
 
+#if __GLASGOW_HASKELL__ >= 810
+import Data.Kind (Type)
+#endif
+
 import Data.GADT.Compare
 import Data.GADT.DeepSeq
 import Data.GADT.Show
 
+
 -- $setup
 -- >>> :set -XKindSignatures -XGADTs
 
@@ -73,8 +84,15 @@
 -- >>> read "mkSome TagInt" :: Some Tag
 -- Some TagInt
 --
+#if __GLASGOW_HASKELL__ >= 810
+type Some :: (k -> Type) -> Type
+#endif
 data Some tag where
     Some :: tag a -> Some tag
+
+#if __GLASGOW_HASKELL__ >= 708
+type role Some representational
+#endif
 
 -- | Constructor.
 mkSome :: tag a -> Some tag
diff --git a/src/Data/Some/Newtype.hs b/src/Data/Some/Newtype.hs
--- a/src/Data/Some/Newtype.hs
+++ b/src/Data/Some/Newtype.hs
@@ -4,9 +4,15 @@
 #if __GLASGOW_HASKELL__ >= 801
 {-# LANGUAGE PatternSynonyms #-}
 #endif
+#if __GLASGOW_HASKELL__ >= 708
+{-# LANGUAGE RoleAnnotations #-}
+#endif
 #if __GLASGOW_HASKELL__ >= 706
 {-# LANGUAGE PolyKinds       #-}
 #endif
+#if __GLASGOW_HASKELL__ >= 810
+{-# LANGUAGE StandaloneKindSignatures #-}
+#endif
 #if __GLASGOW_HASKELL__ >= 702
 {-# LANGUAGE Trustworthy     #-}
 #endif
@@ -31,6 +37,10 @@
 import GHC.Exts            (Any)
 import Unsafe.Coerce       (unsafeCoerce)
 
+#if __GLASGOW_HASKELL__ >= 810
+import Data.Kind (Type)
+#endif
+
 import Data.GADT.Compare
 import Data.GADT.DeepSeq
 import Data.GADT.Show
@@ -80,7 +90,14 @@
 -- >>> read "mkSome TagInt" :: Some Tag
 -- Some TagInt
 --
+#if __GLASGOW_HASKELL__ >= 810
+type Some :: (k -> Type) -> Type
+#endif
 newtype Some tag = UnsafeSome (tag Any)
+
+#if __GLASGOW_HASKELL__ >= 708
+type role Some representational
+#endif
  
 #if __GLASGOW_HASKELL__ >= 801
 {-# COMPLETE Some #-}