diff --git a/src/runtime/store/index.ts b/src/runtime/store/index.ts
index 25c37945c6..98761b847f 100644
--- a/src/runtime/store/index.ts
+++ b/src/runtime/store/index.ts
@@ -85,7 +85,7 @@ export function writable<T>(value: T, start: StartStopNotifier<T> = noop): Writa
 	}
 
 	function update(fn: Updater<T>): void {
-		return set(fn(value));
+		set(fn(value));
 	}
 
 	function subscribe(run: Subscriber<T>, invalidate: Invalidator<T> = noop): Unsubscriber {