diff --git a/src/runtime/internal/lifecycle.ts b/src/runtime/internal/lifecycle.ts
index 9e65e59cbd..4a7616bdea 100644
--- a/src/runtime/internal/lifecycle.ts
+++ b/src/runtime/internal/lifecycle.ts
@@ -11,19 +11,19 @@ export function get_current_component() {
 	return current_component;
 }
 
-export function beforeUpdate(fn) {
+export function beforeUpdate(fn: () => any) {
 	get_current_component().$$.before_update.push(fn);
 }
 
-export function onMount(fn) {
+export function onMount(fn: () => any) {
 	get_current_component().$$.on_mount.push(fn);
 }
 
-export function afterUpdate(fn) {
+export function afterUpdate(fn: () => any) {
 	get_current_component().$$.after_update.push(fn);
 }
 
-export function onDestroy(fn) {
+export function onDestroy(fn: () => any) {
 	get_current_component().$$.on_destroy.push(fn);
 }