diff --git a/.changeset/odd-trees-visit.md b/.changeset/odd-trees-visit.md
new file mode 100644
index 000000000000..ad3c47459fba
--- /dev/null
+++ b/.changeset/odd-trees-visit.md
@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+Allow actions to return undefined
diff --git a/packages/kit/src/index/private.js b/packages/kit/src/index/private.js
index e2f45c5f165d..912572472dff 100644
--- a/packages/kit/src/index/private.js
+++ b/packages/kit/src/index/private.js
@@ -3,6 +3,8 @@ export class HttpError {
 	// include a stack for these sorts of errors, but we also don't want red
 	// squigglies everywhere, so this feels like a not-terribile compromise
 	name = 'HttpError';
+
+	/** @type {void} */
 	stack = undefined;
 
 	/**
diff --git a/packages/kit/src/runtime/server/page/index.js b/packages/kit/src/runtime/server/page/index.js
index fc84e687d079..e1eaa4547e4d 100644
--- a/packages/kit/src/runtime/server/page/index.js
+++ b/packages/kit/src/runtime/server/page/index.js
@@ -364,21 +364,16 @@ export async function handle_json_request(event, options, mod) {
 			return json(result);
 		}
 
-		if (method === 'POST') {
+		if (result?.errors) {
 			// @ts-ignore
-			if (result.errors) {
-				// @ts-ignore
-				return json({ errors: result.errors }, { status: result.status || 400 });
-			}
-
-			return new Response(undefined, {
-				status: 201,
-				// @ts-ignore
-				headers: result.location ? { location: result.location } : undefined
-			});
+			return json({ errors: result.errors }, { status: result.status || 400 });
 		}
 
-		return new Response(undefined, { status: 204 });
+		return new Response(undefined, {
+			status: 204,
+			// @ts-ignore
+			headers: result?.location ? { location: result.location } : undefined
+		});
 	} catch (e) {
 		const error = normalize_error(e);
 
diff --git a/packages/kit/test/apps/basics/src/routes/shadowed/simple/post/+page.server.js b/packages/kit/test/apps/basics/src/routes/shadowed/simple/post/+page.server.js
new file mode 100644
index 000000000000..fee7fff4e694
--- /dev/null
+++ b/packages/kit/test/apps/basics/src/routes/shadowed/simple/post/+page.server.js
@@ -0,0 +1,2 @@
+/** @type {import('./$types').Action} */
+export function POST() {}
diff --git a/packages/kit/test/apps/basics/src/routes/shadowed/simple/post/+page.svelte b/packages/kit/test/apps/basics/src/routes/shadowed/simple/post/+page.svelte
new file mode 100644
index 000000000000..e69de29bb2d1
diff --git a/packages/kit/test/apps/basics/test/server.test.js b/packages/kit/test/apps/basics/test/server.test.js
index e54dfb7eb681..45615bcb5630 100644
--- a/packages/kit/test/apps/basics/test/server.test.js
+++ b/packages/kit/test/apps/basics/test/server.test.js
@@ -257,6 +257,17 @@ test.describe('Shadowed pages', () => {
 
 		expect(await response.json()).toEqual({ answer: 42 });
 	});
+
+	test('Action can return undefined', async ({ request }) => {
+		const response = await request.post('/shadowed/simple/post', {
+			headers: {
+				accept: 'application/json'
+			}
+		});
+
+		expect(response.status()).toBe(204);
+		expect(await response.text()).toEqual('');
+	});
 });
 
 test.describe('Static files', () => {
diff --git a/packages/migrate/migrations/routes/migrate_page_js/index.spec.js b/packages/migrate/migrations/routes/migrate_page_js/index.spec.js
index 0ac56c8d2fa4..48b543509920 100644
--- a/packages/migrate/migrations/routes/migrate_page_js/index.spec.js
+++ b/packages/migrate/migrations/routes/migrate_page_js/index.spec.js
@@ -5,7 +5,7 @@ import { migrate_page } from './index.js';
 
 for (const sample of read_samples(import.meta.url)) {
 	test(sample.description, () => {
-		const actual = migrate_page(sample.before);
+		const actual = migrate_page(sample.before, sample.filename ?? '+page.js');
 		assert.equal(actual, sample.after);
 	});
 }
diff --git a/packages/migrate/migrations/routes/utils.js b/packages/migrate/migrations/routes/utils.js
index 23dd1183d503..8152f9d9114b 100644
--- a/packages/migrate/migrations/routes/utils.js
+++ b/packages/migrate/migrations/routes/utils.js
@@ -472,7 +472,9 @@ export function read_samples(test_file) {
  * @param {string} new_type
  */
 export function rewrite_type(node, code, old_type, new_type) {
+	// @ts-ignore
 	if (node.jsDoc) {
+		// @ts-ignore
 		for (const comment of node.jsDoc) {
 			const str = comment.getText();
 			const index = str.indexOf(old_type);