diff --git a/packages/svelte/src/runtime/internal/lifecycle.js b/packages/svelte/src/runtime/internal/lifecycle.js
index 27c8f67d11..e41d59059e 100644
--- a/packages/svelte/src/runtime/internal/lifecycle.js
+++ b/packages/svelte/src/runtime/internal/lifecycle.js
@@ -36,9 +36,7 @@ export function beforeUpdate(fn) {
  *
  * https://svelte.dev/docs#run-time-svelte-onmount
  * @template T
- * @param {() => T extends Promise<() => any>
- * 		? "Returning a function asynchronously from onMount won't call that function on destroy"
- * 		: T} fn
+ * @param {() => import('./private.js').NotFunction<T> | Promise<import('./private.js').NotFunction<T>> | (() => any)} fn
  * @returns {void}
  */
 export function onMount(fn) {
diff --git a/packages/svelte/src/runtime/internal/private.d.ts b/packages/svelte/src/runtime/internal/private.d.ts
index 50f4a9046b..ef2245256e 100644
--- a/packages/svelte/src/runtime/internal/private.d.ts
+++ b/packages/svelte/src/runtime/internal/private.d.ts
@@ -123,3 +123,8 @@ export interface Task {
 	abort(): void;
 	promise: Promise<void>;
 }
+
+/**
+ * Anything except a function
+ */
+type NotFunction<T> = T extends Function ? never : T;
diff --git a/packages/svelte/test/types/on-mount.ts b/packages/svelte/test/types/on-mount.ts
index 5f5dac71ee..a7271a28c1 100644
--- a/packages/svelte/test/types/on-mount.ts
+++ b/packages/svelte/test/types/on-mount.ts
@@ -51,8 +51,15 @@ onMount(async () => {
 	};
 });
 
-// @ts-expect-error async and return any
+// async and return any
 onMount(async () => {
 	const a: any = null as any;
 	return a;
 });
+
+// async and return function casted to any
+// can't really catch this without also catching above
+onMount(async () => {
+	const a: any = (() => {}) as any;
+	return a;
+});