diff --git a/packages/reactivity/src/watch.ts b/packages/reactivity/src/watch.ts
index 659121ca34b..349f8178d63 100644
--- a/packages/reactivity/src/watch.ts
+++ b/packages/reactivity/src/watch.ts
@@ -42,7 +42,7 @@ export type WatchCallback<V = any, OV = any> = (
   value: V,
   oldValue: OV,
   onCleanup: OnCleanup,
-) => any
+) => void
 
 export type OnCleanup = (cleanupFn: () => void) => void