diff --git a/packages/effect-lens/README.md b/packages/effect-lens/README.md
index 8e641a0..813b7f9 100644
--- a/packages/effect-lens/README.md
+++ b/packages/effect-lens/README.md
@@ -70,8 +70,9 @@ You can get pretty creative! Here's an example of a Lens that points to a specif
 const lens = Effect.all([
     KeyValueStore.KeyValueStore,
     Effect.succeed("someKey"),
+    Effect.makeSemaphore(1),
 ]).pipe(
-    Effect.map(([kv, key]) => Lens.make({
+    Effect.map(([kv, key, semaphore]) => Lens.make({
         get: kv.get(key),
 
         changes: kv.get(key).pipe(
@@ -90,7 +91,7 @@ const lens = Effect.all([
             ? kv.set(key, a.value)
             : kv.remove(key),
 
-        lock: Effect.succeed(effect => effect),
+        lock: Effect.succeed(semaphore.withPermits(1)),
     })),
 
     Effect.provide(BrowserKeyValueStore.layerLocalStorage),