diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,5 +1,9 @@
 # Version history for ral
 
+## 0.2
+
+- Support `fin-0.2`
+
 ## 0.1
 
 - First version. Released on an unsuspecting world.
diff --git a/ral-optics.cabal b/ral-optics.cabal
--- a/ral-optics.cabal
+++ b/ral-optics.cabal
@@ -1,6 +1,6 @@
 cabal-version:      2.2
 name:               ral-optics
-version:            0.1
+version:            0.2
 synopsis:           Length-indexed random access lists: optics utilities.
 category:           Data, Dependent Types, Singletons, Optics
 description:
@@ -13,10 +13,17 @@
 license-file:       LICENSE
 author:             Oleg Grenrus <oleg.grenrus@iki.fi>
 maintainer:         Oleg.Grenrus <oleg.grenrus@iki.fi>
-copyright:          (c) 2019 Oleg Grenrus
+copyright:          (c) 2019-2021 Oleg Grenrus
 build-type:         Simple
 extra-source-files: ChangeLog.md
-tested-with:        GHC ==8.0.2 || ==8.2.2 || ==8.4.4 || ==8.6.5 || ==8.8.1
+tested-with:
+  GHC ==8.0.2
+   || ==8.2.2
+   || ==8.4.4
+   || ==8.6.5
+   || ==8.8.4
+   || ==8.10.4
+   || ==9.0.1
 
 source-repository head
   type:     git
@@ -32,6 +39,7 @@
     Data.RAList.Optics
     Data.RAVec.NonEmpty.Optics
     Data.RAVec.Optics
+    Data.RAVec.Tree.DF.Optics
     Data.RAVec.Tree.Optics
 
   other-modules:
@@ -39,11 +47,11 @@
     Data.RAVec.NonEmpty.Optics.Internal
 
   build-depends:
-    , base         >=4.9   && <4.14
+    , base         >=4.9 && <4.16
     , bin          ^>=0.1
-    , fin          ^>=0.1.1
-    , optics-core  ^>=0.2
-    , ral          ^>=0.1
+    , fin          ^>=0.2
+    , optics-core  >=0.2 && <0.5
+    , ral          ^>=0.2
 
 -- dump-core
 -- if impl(ghc >= 8.0)
diff --git a/src/Data/RAList/NonEmpty/Optics.hs b/src/Data/RAList/NonEmpty/Optics.hs
--- a/src/Data/RAList/NonEmpty/Optics.hs
+++ b/src/Data/RAList/NonEmpty/Optics.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP                   #-}
 {-# LANGUAGE FlexibleInstances     #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
 {-# LANGUAGE RankNTypes            #-}
@@ -27,6 +28,7 @@
 -- Instances
 -------------------------------------------------------------------------------
 
+#if !MIN_VERSION_optics_core(0,4,0)
 instance L.FunctorWithIndex Int NERAList where
     imap = imap
 
@@ -35,6 +37,7 @@
 
 instance L.TraversableWithIndex Int NERAList where
     itraverse = itraverse
+#endif
 
 instance L.Each Int (NERAList a) (NERAList b) a b
 
diff --git a/src/Data/RAList/Optics.hs b/src/Data/RAList/Optics.hs
--- a/src/Data/RAList/Optics.hs
+++ b/src/Data/RAList/Optics.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP                   #-}
 {-# LANGUAGE FlexibleInstances     #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
 {-# LANGUAGE RankNTypes            #-}
@@ -30,6 +31,7 @@
 -- Instances
 -------------------------------------------------------------------------------
 
+#if !MIN_VERSION_optics_core(0,4,0)
 instance L.FunctorWithIndex Int RAList where
     imap = imap
 
@@ -38,6 +40,7 @@
 
 instance L.TraversableWithIndex Int RAList where
     itraverse = itraverse
+#endif
 
 instance L.Each Int (RAList a) (RAList b) a b
 
diff --git a/src/Data/RAVec/NonEmpty/Optics.hs b/src/Data/RAVec/NonEmpty/Optics.hs
--- a/src/Data/RAVec/NonEmpty/Optics.hs
+++ b/src/Data/RAVec/NonEmpty/Optics.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP                   #-}
 {-# LANGUAGE FlexibleInstances     #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
 {-# LANGUAGE TypeFamilies          #-}
@@ -34,6 +35,7 @@
 -- Instances
 -------------------------------------------------------------------------------
 
+#if !MIN_VERSION_optics_core(0,4,0)
 instance L.FunctorWithIndex (PosP b) (NERAVec b) where
     imap = imap
 
@@ -53,6 +55,7 @@
 
 instance L.TraversableWithIndex (PosP' n b) (NERAVec' n b) where
     itraverse = itraverse'
+#endif
 
 instance L.Each (PosP n) (NERAVec n a) (NERAVec n b) a b where
 
diff --git a/src/Data/RAVec/Optics.hs b/src/Data/RAVec/Optics.hs
--- a/src/Data/RAVec/Optics.hs
+++ b/src/Data/RAVec/Optics.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP                   #-}
 {-# LANGUAGE FlexibleInstances     #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
 {-# LANGUAGE TypeFamilies          #-}
@@ -10,6 +11,7 @@
 import Control.Applicative        ((<$>))
 import Data.Bin.Pos               (Pos (..))
 import Data.RAVec.NonEmpty.Optics ()
+import Prelude                    (Functor)
 
 import qualified Data.RAVec.NonEmpty.Optics.Internal as NE
 import qualified Optics.Core                         as L
@@ -20,6 +22,7 @@
 -- >>> import Optics.Core (set)
 -- >>> import Prelude
 -- >>> import qualified Data.Type.Bin as B
+-- >>> import Data.RAVec
 
 -------------------------------------------------------------------------------
 -- Indexing
@@ -40,6 +43,7 @@
 -- Instances
 -------------------------------------------------------------------------------
 
+#if !MIN_VERSION_optics_core(0,4,0)
 instance L.FunctorWithIndex (Pos b) (RAVec b) where
     imap = imap
 
@@ -49,6 +53,7 @@
 
 instance L.TraversableWithIndex (Pos b) (RAVec b) where
     itraverse = itraverse
+#endif
 
 instance L.Each (Pos n) (RAVec n a) (RAVec n b) a b where
 
diff --git a/src/Data/RAVec/Tree/DF/Optics.hs b/src/Data/RAVec/Tree/DF/Optics.hs
new file mode 100644
--- /dev/null
+++ b/src/Data/RAVec/Tree/DF/Optics.hs
@@ -0,0 +1,72 @@
+{-# LANGUAGE CPP                   #-}
+{-# LANGUAGE FlexibleInstances     #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE RankNTypes            #-}
+{-# LANGUAGE TypeFamilies          #-}
+{-# OPTIONS_GHC -fno-warn-orphans #-}
+module Data.RAVec.Tree.DF.Optics (
+    -- * Indexing
+    ix,
+    ) where
+
+import Control.Applicative ((<$>))
+import Data.Wrd            (Wrd (..))
+import Prelude             (Functor)
+
+import qualified Data.Type.Nat as N
+import qualified Optics.Core   as L
+
+import Data.RAVec.Tree.DF
+
+-- $setup
+-- >>> import Optics.Core (set, (&), (.~))
+-- >>> import Prelude
+-- >>> import Data.RAVec.Tree.DF
+-- >>> import Data.Wrd (Wrd (..))
+
+type LensLikeVL f s t a b = (a -> f b) -> s -> f t
+type LensLikeVL' f s a = LensLikeVL f s s a a
+
+-------------------------------------------------------------------------------
+-- Indexing
+-------------------------------------------------------------------------------
+
+-- | Index lens.
+--
+-- >>> let tree = Node (Node (Leaf 'a') (Leaf 'b')) (Node (Leaf 'c') (Leaf 'd'))
+-- >>> tree & ix (W1 $ W0 WE) .~ 'z'
+-- Node (Node (Leaf 'a') (Leaf 'b')) (Node (Leaf 'z') (Leaf 'd'))
+--
+ix :: Wrd n -> L.Lens' (Tree n a) a
+ix i = L.lensVL (ixVL i)
+
+ixVL :: Functor f => Wrd n -> LensLikeVL' f (Tree n a) a
+ixVL WE      f (Leaf x)   = Leaf <$> f x
+ixVL (W0 is) f (Node x y) = (`Node` y) <$> ixVL is f x
+ixVL (W1 is) f (Node x y) = (x `Node`) <$> ixVL is f y
+
+-------------------------------------------------------------------------------
+-- Instances
+-------------------------------------------------------------------------------
+
+#if !MIN_VERSION_optics_core(0,4,0)
+instance N.SNatI n => L.FunctorWithIndex (Wrd n) (Tree n) where
+    imap = imap
+
+instance N.SNatI n => L.FoldableWithIndex (Wrd n) (Tree n) where
+    ifoldMap = ifoldMap
+    ifoldr   = ifoldr
+
+instance N.SNatI n => L.TraversableWithIndex (Wrd n) (Tree n) where
+    itraverse = itraverse
+#endif
+
+instance N.SNatI n => L.Each (Wrd n) (Tree n a) (Tree n b) a b
+
+type instance L.Index (Tree n a)   = Wrd n
+type instance L.IxValue (Tree n a) = a
+
+instance L.Ixed (Tree n a) where
+    type IxKind (Tree n a) = L.A_Lens
+    ix = ix
+
diff --git a/src/Data/RAVec/Tree/Optics.hs b/src/Data/RAVec/Tree/Optics.hs
--- a/src/Data/RAVec/Tree/Optics.hs
+++ b/src/Data/RAVec/Tree/Optics.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP                   #-}
 {-# LANGUAGE FlexibleInstances     #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
 {-# LANGUAGE TypeFamilies          #-}
@@ -18,6 +19,8 @@
 -- $setup
 -- >>> import Optics.Core (set)
 -- >>> import Prelude
+-- >>> import Data.RAVec.Tree
+-- >>> import Data.Wrd (Wrd (..))
 
 type LensLikeVL f s t a b = (a -> f b) -> s -> f t
 type LensLikeVL' f s a = LensLikeVL f s s a a
@@ -44,6 +47,7 @@
 -- Instances
 -------------------------------------------------------------------------------
 
+#if !MIN_VERSION_optics_core(0,4,0)
 instance L.FunctorWithIndex (Wrd n) (Tree n) where
     imap = imap
 
@@ -53,6 +57,7 @@
 
 instance L.TraversableWithIndex (Wrd n) (Tree n) where
     itraverse = itraverse
+#endif
 
 instance L.Each (Wrd n) (Tree n a) (Tree n b) a b where