diff --git a/CHANGELOG.md b/CHANGELOG.md
index 518fa2e..627a9a1 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,6 @@
 ## Unreleased
 
+- Fixed incorrect TypeScript definition for async `derived` ([#25](https://github.com/PixievoltNo1/svelte-writable-derived/issues/25))
 - Now supports Svelte 5 (-next.94 and later)
 
 In Svelte 5, this package does not use runes and continues to use the original writable store interface, which is not deprecated. I may release a separate package that uses runes.
diff --git a/index.d.ts b/index.d.ts
index 79782a4..b2dbfff 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -42,7 +42,7 @@ export default function writableDerived<S extends Stores, T>(
 
 export default function writableDerived<S extends Stores, T>(
     origins: S,
-    derive: (values: StoresValues<S>, set: (value: T) => void, update: Updater<T>) => void,
+    derive: (values: StoresValues<S>, set: (value: T) => void, update: (fn: Updater<T>) => void) => void,
     reflect: (reflecting: T, old: StoresValues<S>) => SetValues<S>,
     initial?: T
 ): Writable<T>;