diff --git a/src/runtime/internal/lifecycle.ts b/src/runtime/internal/lifecycle.ts
index 258f8b651d..99f605daa4 100644
--- a/src/runtime/internal/lifecycle.ts
+++ b/src/runtime/internal/lifecycle.ts
@@ -31,7 +31,7 @@ export function beforeUpdate(fn: () => any) {
  * 
  * https://svelte.dev/docs#run-time-svelte-onmount
  */
-export function onMount<T>(fn: (() =>  T extends Promise<void> ? T : T extends Promise<unknown> ? never : T)): void {
+export function onMount<T>(fn: () => T extends Promise<() => any> ? never : T): void {
 	get_current_component().$$.on_mount.push(fn);
 }