diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,14 +1,18 @@
+# 0.4.3.5
+
+* [#131](https://github.com/stevenfontanella/microlens/issues/131) Add `At` and `Ixed` instance for `HashSet`.
+
 # 0.4.3.4
 
-* [#171](https://github.com/stevenfontanella/microlens/pull/171) Support text 2.1
+* [#171](https://github.com/stevenfontanella/microlens/pull/171) Support text 2.1.
 
 # 0.4.3.3
 
-* [#161](https://github.com/stevenfontanella/microlens/pull/161) Fix GHC 9.4 warning for using `~` without TypeOperators
+* [#161](https://github.com/stevenfontanella/microlens/pull/161) Fix GHC 9.4 warning for using `~` without TypeOperators.
 
 # 0.4.3.2
 
-* [#156](https://github.com/stevenfontanella/microlens/pull/156) Add a missing upper bound for text dependency
+* [#156](https://github.com/stevenfontanella/microlens/pull/156) Add a missing upper bound for text dependency.
 
 # 0.4.3.1
 
diff --git a/microlens-platform.cabal b/microlens-platform.cabal
--- a/microlens-platform.cabal
+++ b/microlens-platform.cabal
@@ -1,5 +1,5 @@
 name:                microlens-platform
-version:             0.4.3.4
+version:             0.4.3.5
 synopsis:            microlens + all batteries included (best for apps)
 description:
   This package exports a module which is the recommended starting point for using <http://hackage.haskell.org/package/microlens microlens> if you aren't trying to keep your dependencies minimal. By importing @Lens.Micro.Platform@ you get all functions and instances from <http://hackage.haskell.org/package/microlens microlens>, <http://hackage.haskell.org/package/microlens-th microlens-th>, <http://hackage.haskell.org/package/microlens-mtl microlens-mtl>, <http://hackage.haskell.org/package/microlens-ghc microlens-ghc>, as well as instances for @Vector@, @Text@, and @HashMap@.
diff --git a/src/Lens/Micro/Platform.hs b/src/Lens/Micro/Platform.hs
--- a/src/Lens/Micro/Platform.hs
+++ b/src/Lens/Micro/Platform.hs
@@ -55,8 +55,10 @@
 import Data.Hashable
 import Data.Int
 import Data.Monoid
+import Data.Functor (($>))
 
 import Data.HashMap.Lazy as HashMap
+import Data.HashSet as HashSet
 import Data.Vector as Vector
 import Data.Vector.Primitive as Prim
 import Data.Vector.Storable as Storable
@@ -73,6 +75,9 @@
 
 type instance Index   (HashMap k a) = k
 type instance IxValue (HashMap k a) = a
+type instance Index   (HashSet a) = a
+type instance IxValue (HashSet a) = ()
+type instance IxValue (HashMap k a) = a
 type instance Index   (Vector.Vector a) = Int
 type instance IxValue (Vector.Vector a) = a
 type instance Index   (Prim.Vector a) = Int
@@ -97,6 +102,16 @@
     Nothing -> maybe m (const (HashMap.delete k m)) mv
     Just v' -> HashMap.insert k v' m
     where mv = HashMap.lookup k m
+  {-# INLINE at #-}
+
+instance (Eq k, Hashable k) => Ixed (HashSet k) where
+  ix k f m = if HashSet.member k m
+     then f () $> m
+     else pure m
+  {-# INLINE ix #-}
+
+instance (Eq k, Hashable k) => At (HashSet k) where
+  at k f s = HashSet.fromMap <$> HashMap.alterF f k (HashSet.toMap s)
   {-# INLINE at #-}
 
 instance Ixed (Vector.Vector a) where