diff --git a/CHANGELOG.md b/CHANGELOG.md
new file mode 100644
--- /dev/null
+++ b/CHANGELOG.md
@@ -0,0 +1,3 @@
+0.3.0.2
+-------
+* GHC 8 compatibility
diff --git a/generic-trie.cabal b/generic-trie.cabal
--- a/generic-trie.cabal
+++ b/generic-trie.cabal
@@ -1,5 +1,5 @@
 name:                generic-trie
-version:             0.3.0.1
+version:             0.3.0.2
 synopsis:            A map, where the keys may be complex structured data.
 description:         This type implements maps where the keys are themselves
                      complex structured data.  For example, the keys may be
@@ -19,11 +19,14 @@
 homepage:            http://github.com/glguy/tries
 bug-reports:         http://github.com/glguy/tries/issues
 
+extra-source-files:
+  CHANGELOG.md
+
 library
   exposed-modules:     Data.GenericTrie,
                        Data.GenericTrie.Internal
-  build-depends:       base             >= 4.5     && < 4.9,
-                       transformers     >= 0.2     && < 0.5,
+  build-depends:       base             >= 4.5     && < 4.10,
+                       transformers     >= 0.2     && < 0.6,
                        containers       >= 0.4.2.1 && < 0.6
   GHC-options:         -O2 -Wall
 
diff --git a/src/Data/GenericTrie.hs b/src/Data/GenericTrie.hs
--- a/src/Data/GenericTrie.hs
+++ b/src/Data/GenericTrie.hs
@@ -46,7 +46,7 @@
   , insertWith
   , insertWith'
   , delete
-  , at 
+  , at
 
   -- ** Queries
   , member
@@ -124,8 +124,12 @@
 
 -- | Lens for the value at a given key
 at :: (Functor f, TrieKey k) => k -> (Maybe a -> f (Maybe a)) -> Trie k a -> f (Trie k a)
-at = trieAt
-{-# INLINE at #-}
+at k f m = fmap aux (f mv)
+  where
+  mv = lookup k m
+  aux r = case r of
+    Nothing -> maybe m (const (delete k m)) mv
+    Just v' -> insert k v' m
 
 -- | Insert an element into a trie
 insert :: TrieKey k => k -> a -> Trie k a -> Trie k a
diff --git a/src/Data/GenericTrie/Internal.hs b/src/Data/GenericTrie/Internal.hs
--- a/src/Data/GenericTrie/Internal.hs
+++ b/src/Data/GenericTrie/Internal.hs
@@ -6,7 +6,12 @@
 {-# LANGUAGE FlexibleInstances #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE Trustworthy #-} -- coerce
+{-# LANGUAGE CPP #-} -- MProxy on ghc >= 8
 
+#if MIN_VERSION_base(4,9,0)
+{-# LANGUAGE DataKinds #-} -- Meta
+#endif
+
 -- | Unstable implementation details
 module Data.GenericTrie.Internal
   ( TrieKey(..)
@@ -23,7 +28,6 @@
   , genericMapMaybeWithKey
   , genericSingleton
   , genericEmpty
-  , genericAt
   , genericFoldWithKey
   , genericTraverseWithKey
   , TrieRepDefault
@@ -70,9 +74,6 @@
   -- | Delete element from trie
   trieDelete :: k -> Trie k a -> Trie k a
 
-  trieAt :: Functor f => k -> (Maybe a -> f (Maybe a)) ->
-                              Trie k a -> f (Trie k a)
-
   -- | Construct a trie holding a single value
   trieSingleton :: k -> a -> Trie k a
 
@@ -171,11 +172,6 @@
     Trie k a -> Trie k b -> Trie k c
   trieMergeWithKey = genericMergeWithKey
 
-  default trieAt ::
-    ( GTrieKey (Rep k) , TrieRep k ~ TrieRepDefault k, Generic k, Functor f ) =>
-    k -> (Maybe a -> f (Maybe a)) -> Trie k a -> f (Trie k a)
-  trieAt = genericAt
-
 -- | The default implementation of a 'TrieRep' is 'GTrie' wrapped in
 -- a 'Maybe'. This wrapping is due to the 'GTrie' being a non-empty
 -- trie allowing all the of the "emptiness" to be represented at the
@@ -190,15 +186,6 @@
 -- Manually derived instances for base types
 ------------------------------------------------------------------------------
 
-simpleAt ::
-  (Functor f, TrieKey k) =>
-  k -> (Maybe a -> f (Maybe a)) -> Trie k a -> f (Trie k a)
-simpleAt k f m = flip fmap (f mv) $ \r -> case r of
-    Nothing -> maybe m (const (trieDelete k m)) mv
-    Just v' -> trieInsert k v' m
-    where mv = trieLookup k m
-{-# INLINE simpleAt #-}
-
 -- | 'Int' tries are implemented with 'IntMap'.
 instance TrieKey Int where
   type TrieRep Int              = IntMap
@@ -215,20 +202,19 @@
   trieFoldWithKey f z (MkTrie x)    = IntMap.foldWithKey f z x
   trieTraverseWithKey f (MkTrie x)  = fmap MkTrie (IntMap.traverseWithKey f x)
   trieMergeWithKey f g h (MkTrie x) (MkTrie y) = MkTrie (IntMap.mergeWithKey f (coerce g) (coerce h) x y)
-  trieAt                        = simpleAt
-  {-# INLINE trieEmpty #-}
-  {-# INLINE trieInsert #-}
-  {-# INLINE trieLookup #-}
-  {-# INLINE trieDelete #-}
-  {-# INLINE trieSingleton #-}
-  {-# INLINE trieFoldWithKey #-}
-  {-# INLINE trieShowsPrec #-}
-  {-# INLINE trieTraverse #-}
-  {-# INLINE trieTraverseWithKey #-}
-  {-# INLINE trieNull #-}
-  {-# INLINE trieMap #-}
-  {-# INLINE trieMergeWithKey #-}
-  {-# INLINE trieMapMaybeWithKey #-}
+  {-# INLINABLE trieEmpty #-}
+  {-# INLINABLE trieInsert #-}
+  {-# INLINABLE trieLookup #-}
+  {-# INLINABLE trieDelete #-}
+  {-# INLINABLE trieSingleton #-}
+  {-# INLINABLE trieFoldWithKey #-}
+  {-# INLINABLE trieShowsPrec #-}
+  {-# INLINABLE trieTraverse #-}
+  {-# INLINABLE trieTraverseWithKey #-}
+  {-# INLINABLE trieNull #-}
+  {-# INLINABLE trieMap #-}
+  {-# INLINABLE trieMergeWithKey #-}
+  {-# INLINABLE trieMapMaybeWithKey #-}
 
 -- | 'Integer' tries are implemented with 'Map'.
 instance TrieKey Integer where
@@ -246,20 +232,19 @@
   trieFoldWithKey f z (MkTrie x)    = Map.foldrWithKey f z x
   trieTraverseWithKey f (MkTrie x)  = fmap MkTrie (Map.traverseWithKey f x)
   trieMergeWithKey f g h (MkTrie x) (MkTrie y) = MkTrie (Map.mergeWithKey f (coerce g) (coerce h) x y)
-  trieAt                            = simpleAt
-  {-# INLINE trieEmpty #-}
-  {-# INLINE trieInsert #-}
-  {-# INLINE trieLookup #-}
-  {-# INLINE trieDelete #-}
-  {-# INLINE trieSingleton #-}
-  {-# INLINE trieFoldWithKey #-}
-  {-# INLINE trieShowsPrec #-}
-  {-# INLINE trieTraverse #-}
-  {-# INLINE trieTraverseWithKey #-}
-  {-# INLINE trieNull #-}
-  {-# INLINE trieMap #-}
-  {-# INLINE trieMergeWithKey #-}
-  {-# INLINE trieMapMaybeWithKey #-}
+  {-# INLINABLE trieEmpty #-}
+  {-# INLINABLE trieInsert #-}
+  {-# INLINABLE trieLookup #-}
+  {-# INLINABLE trieDelete #-}
+  {-# INLINABLE trieSingleton #-}
+  {-# INLINABLE trieFoldWithKey #-}
+  {-# INLINABLE trieShowsPrec #-}
+  {-# INLINABLE trieTraverse #-}
+  {-# INLINABLE trieTraverseWithKey #-}
+  {-# INLINABLE trieNull #-}
+  {-# INLINABLE trieMap #-}
+  {-# INLINABLE trieMergeWithKey #-}
+  {-# INLINABLE trieMapMaybeWithKey #-}
 
 -- | 'Char' tries are implemented with 'IntMap'.
 instance TrieKey Char where
@@ -277,20 +262,19 @@
   trieFoldWithKey f z (MkTrie x)    = IntMap.foldrWithKey (f . chr) z x
   trieTraverseWithKey f (MkTrie x)  = fmap MkTrie (IntMap.traverseWithKey (f . chr) x)
   trieMergeWithKey f g h (MkTrie x) (MkTrie y) = MkTrie (IntMap.mergeWithKey (f . chr) (coerce g) (coerce h) x y)
-  trieAt                            = simpleAt
-  {-# INLINE trieEmpty #-}
-  {-# INLINE trieInsert #-}
-  {-# INLINE trieLookup #-}
-  {-# INLINE trieDelete #-}
-  {-# INLINE trieSingleton #-}
-  {-# INLINE trieFoldWithKey #-}
-  {-# INLINE trieShowsPrec #-}
-  {-# INLINE trieTraverse #-}
-  {-# INLINE trieTraverseWithKey #-}
-  {-# INLINE trieNull #-}
-  {-# INLINE trieMap #-}
-  {-# INLINE trieMergeWithKey #-}
-  {-# INLINE trieMapMaybeWithKey #-}
+  {-# INLINABLE trieEmpty #-}
+  {-# INLINABLE trieInsert #-}
+  {-# INLINABLE trieLookup #-}
+  {-# INLINABLE trieDelete #-}
+  {-# INLINABLE trieSingleton #-}
+  {-# INLINABLE trieFoldWithKey #-}
+  {-# INLINABLE trieShowsPrec #-}
+  {-# INLINABLE trieTraverse #-}
+  {-# INLINABLE trieTraverseWithKey #-}
+  {-# INLINABLE trieNull #-}
+  {-# INLINABLE trieMap #-}
+  {-# INLINABLE trieMergeWithKey #-}
+  {-# INLINABLE trieMapMaybeWithKey #-}
 
 -- | Tries indexed by 'OrdKey' will be represented as an ordinary 'Map'
 -- and the keys will be compared based on the 'Ord' instance for @k@.
@@ -316,20 +300,19 @@
   trieFoldWithKey f z (MkTrie x)        = Map.foldrWithKey (f . OrdKey) z x
   trieTraverseWithKey f (MkTrie x)      = fmap MkTrie (Map.traverseWithKey (f . OrdKey) x)
   trieMergeWithKey f g h (MkTrie x) (MkTrie y) = MkTrie (Map.mergeWithKey (f . OrdKey) (coerce g) (coerce h) x y)
-  trieAt                                = simpleAt
-  {-# INLINE trieEmpty #-}
-  {-# INLINE trieInsert #-}
-  {-# INLINE trieLookup #-}
-  {-# INLINE trieDelete #-}
-  {-# INLINE trieSingleton #-}
-  {-# INLINE trieFoldWithKey #-}
-  {-# INLINE trieShowsPrec #-}
-  {-# INLINE trieTraverse #-}
-  {-# INLINE trieTraverseWithKey #-}
-  {-# INLINE trieNull #-}
-  {-# INLINE trieMap #-}
-  {-# INLINE trieMergeWithKey #-}
-  {-# INLINE trieMapMaybeWithKey #-}
+  {-# INLINABLE trieEmpty #-}
+  {-# INLINABLE trieInsert #-}
+  {-# INLINABLE trieLookup #-}
+  {-# INLINABLE trieDelete #-}
+  {-# INLINABLE trieSingleton #-}
+  {-# INLINABLE trieFoldWithKey #-}
+  {-# INLINABLE trieShowsPrec #-}
+  {-# INLINABLE trieTraverse #-}
+  {-# INLINABLE trieTraverseWithKey #-}
+  {-# INLINABLE trieNull #-}
+  {-# INLINABLE trieMap #-}
+  {-# INLINABLE trieMergeWithKey #-}
+  {-# INLINABLE trieMapMaybeWithKey #-}
 
 ------------------------------------------------------------------------------
 -- Automatically derived instances for common types
@@ -384,19 +367,6 @@
 {-# INLINABLE genericEmpty #-}
 
 -- | Generic implementation of 'insert'. This is the default implementation.
-genericAt ::
-    ( GTrieKey (Rep k), Generic k
-    , TrieRep k ~ TrieRepDefault k
-    , Functor f
-    ) =>
-    k -> (Maybe a -> f (Maybe a)) -> Trie k a -> f (Trie k a)
-genericAt k f (MkTrie (Compose m)) =
-  case m of
-    Nothing -> fmap (MkTrie . Compose . fmap (gtrieSingleton (from k))) (f Nothing)
-    Just t  -> gtrieAt (MkTrie . Compose) (from k) f t
-{-# INLINABLE genericAt #-}
-
--- | Generic implementation of 'insert'. This is the default implementation.
 genericInsert ::
     ( GTrieKey (Rep k), Generic k
     , TrieRep k ~ TrieRepDefault k
@@ -533,11 +503,6 @@
                     (GTrie f a -> Maybe (GTrie f c)) ->
                     (GTrie f b -> Maybe (GTrie f c)) ->
                     GTrie f a -> GTrie f b -> Maybe (GTrie f c)
-  gtrieAt        :: Functor m =>
-                      (Maybe (GTrie f a) -> r) ->
-                      f p ->
-                      (Maybe a -> m (Maybe a)) ->
-                      GTrie f a -> m r
 
 -- | The 'GTrieKeyShow' class provides generic implementations
 -- of 'showsPrec'. This class is separate due to its implementation
@@ -561,7 +526,6 @@
   gfoldWithKey f z (MTrie x)    = gfoldWithKey (f . M1) z x
   gtraverseWithKey f (MTrie x)  = fmap MTrie (gtraverseWithKey (f . M1) x)
   gmergeWithKey f g h (MTrie x) (MTrie y) = fmap MTrie (gmergeWithKey (f . M1) (coerce g) (coerce h) x y)
-  gtrieAt z (M1 k) f (MTrie x)  = gtrieAt (z . fmap MTrie) k f x
   {-# INLINE gtrieLookup #-}
   {-# INLINE gtrieInsert #-}
   {-# INLINE gtrieSingleton #-}
@@ -571,9 +535,12 @@
   {-# INLINE gtrieTraverse #-}
   {-# INLINE gfoldWithKey #-}
   {-# INLINE gtraverseWithKey #-}
-  {-# INLINE gtrieAt #-}
 
-data MProxy c (f :: * -> *) a = MProxy
+#if MIN_VERSION_base(4,9,0)
+data MProxy (c :: Meta) (f :: * -> *) a = MProxy
+#else
+data MProxy (c :: *)    (f :: * -> *) a = MProxy
+#endif
 
 instance GTrieKeyShow f => GTrieKeyShow (M1 D d f) where
   gtrieShowsPrec p (MTrie x)    = showsPrec p x
@@ -614,7 +581,6 @@
      h' t = case h (KTrie t) of
               Just (KTrie t') -> t'
               Nothing         -> trieEmpty
-  gtrieAt z (K1 k) f (KTrie x) = fmap (z . fmap KTrie . checkNull) (trieAt k f x)
   {-# INLINE gtrieLookup #-}
   {-# INLINE gtrieInsert #-}
   {-# INLINE gtrieSingleton #-}
@@ -625,7 +591,6 @@
   {-# INLINE gtraverseWithKey #-}
   {-# INLINE gmergeWithKey #-}
   {-# INLINE gmapMaybeWithKey #-}
-  {-# INLINE gtrieAt #-}
 
 instance TrieKey k => GTrieKeyShow (K1 i k) where
   gtrieShowsPrec p (KTrie x)            = showsPrec p x
@@ -672,12 +637,6 @@
     h' i t = do PTrie t' <- h (PTrie (gtrieSingleton i t))
                 gtrieLookup i t'
 
-  gtrieAt z (i :*: j) f (PTrie t) = gtrieAt (z . fmap PTrie) i f1 t
-    where
-    f1 Nothing = fmap (fmap (gtrieSingleton j)) (f Nothing)
-    f1 (Just ti) = gtrieAt id j f ti
-
-
   {-# INLINE gtrieLookup #-}
   {-# INLINE gtrieInsert #-}
   {-# INLINE gtrieDelete #-}
@@ -688,7 +647,6 @@
   {-# INLINE gtraverseWithKey #-}
   {-# INLINE gmergeWithKey #-}
   {-# INLINE gmapMaybeWithKey #-}
-  {-# INLINE gtrieAt #-}
 
 instance (GTrieKeyShow f, GTrieKeyShow g) => GTrieKeyShow (f :*: g) where
   gtrieShowsPrec p (PTrie x)            = showsPrec p x
@@ -785,13 +743,6 @@
     hr t = do STrieR t' <- h (STrieR t)
               return t'
 
-  gtrieAt z (L1 k) f (STrieL x)   = gtrieAt (z . fmap STrieL) k f x
-  gtrieAt z (R1 k) f (STrieR y)   = gtrieAt (z . fmap STrieR) k f y
-  gtrieAt z (L1 k) f (STrieR y)   = fmap (z . Just . maybe (STrieR y) (\v -> STrieB (gtrieSingleton k v) y)) (f Nothing)
-  gtrieAt z (R1 k) f (STrieL x)   = fmap (z . Just . maybe (STrieL x) (\v -> STrieB x (gtrieSingleton k v))) (f Nothing)
-  gtrieAt z (L1 k) f (STrieB x y) = gtrieAt (z . Just . maybe (STrieR y) (`STrieB` y)) k f x
-  gtrieAt z (R1 k) f (STrieB x y) = gtrieAt (z . Just . maybe (STrieL x) (x `STrieB`)) k f y
-
   {-# INLINE gtrieLookup #-}
   {-# INLINE gtrieInsert #-}
   {-# INLINE gtrieDelete #-}
@@ -802,7 +753,6 @@
   {-# INLINE gtraverseWithKey #-}
   {-# INLINE gmergeWithKey #-}
   {-# INLINE gmapMaybeWithKey #-}
-  {-# INLINE gtrieAt #-}
 
 instance (GTrieKeyShow f, GTrieKeyShow g) => GTrieKeyShow (f :+: g) where
   gtrieShowsPrec p (STrieB x y)         = showParen (p > 10)
@@ -833,7 +783,6 @@
   gfoldWithKey f z (UTrie x)    = f U1 x z
   gtraverseWithKey f (UTrie x)  = fmap UTrie (f U1 x)
   gmergeWithKey f _ _ (UTrie x) (UTrie y) = fmap UTrie (f U1 x y)
-  gtrieAt z _ f (UTrie x)       = fmap (z . fmap UTrie) (f (Just x))
   {-# INLINE gtrieLookup #-}
   {-# INLINE gtrieInsert #-}
   {-# INLINE gtrieDelete #-}
@@ -844,7 +793,6 @@
   {-# INLINE gtraverseWithKey #-}
   {-# INLINE gmergeWithKey #-}
   {-# INLINE gmapMaybeWithKey #-}
-  {-# INLINE gtrieAt #-}
 
 instance GTrieKeyShow U1 where
   gtrieShowsPrec p (UTrie x)    = showsPrec p x
@@ -865,7 +813,6 @@
   gfoldWithKey _ _ t            = t `seq` error "GTrieKey.V1: gmapFoldWithKey"
   gtraverseWithKey _ t          = t `seq` error "GTrieKey.V1: gtraverseWithKey"
   gmergeWithKey _ _ _ t u       = t `seq` u `seq` error "GTrieKey.V1: gmergeWithKey"
-  gtrieAt _ k _ t               = k `seq` t `seq` error "GTrieKey.V1: gtrieAt"
   {-# INLINE gtrieLookup #-}
   {-# INLINE gtrieInsert #-}
   {-# INLINE gtrieDelete #-}
@@ -876,7 +823,6 @@
   {-# INLINE gtraverseWithKey #-}
   {-# INLINE gmergeWithKey #-}
   {-# INLINE gmapMaybeWithKey #-}
-  {-# INLINE gtrieAt #-}
 
 instance GTrieKeyShow V1 where
   gtrieShowsPrec _ _            = showString "()"