diff --git a/src/runtime/internal/lifecycle.ts b/src/runtime/internal/lifecycle.ts
index d5938874fc..a8e37e9632 100644
--- a/src/runtime/internal/lifecycle.ts
+++ b/src/runtime/internal/lifecycle.ts
@@ -30,7 +30,7 @@ export function onDestroy(fn) {
 export function createEventDispatcher() {
 	const component = get_current_component();
 
-	return (type, detail) => {
+	return (type: string, detail?: any) => {
 		const callbacks = component.$$.callbacks[type];
 
 		if (callbacks) {