diff --git a/.changeset/hot-shoes-bow.md b/.changeset/hot-shoes-bow.md
new file mode 100644
index 000000000000..5a3a6794aef1
--- /dev/null
+++ b/.changeset/hot-shoes-bow.md
@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+Fix parsing content-type header for actions
diff --git a/packages/kit/src/runtime/server/index.js b/packages/kit/src/runtime/server/index.js
index 6f08b62f1dcc..8eb14c6da13f 100644
--- a/packages/kit/src/runtime/server/index.js
+++ b/packages/kit/src/runtime/server/index.js
@@ -3,6 +3,7 @@ import { render_page } from './page/index.js';
 import { render_response } from './page/render.js';
 import { respond_with_error } from './page/respond_with_error.js';
 import { coalesce_to_error } from '../../utils/error.js';
+import { is_form_content_type } from '../../utils/http.js';
 import { GENERIC_ERROR, handle_fatal_error } from './utils.js';
 import { decode_params, disable_search, normalize_path } from '../../utils/url.js';
 import { exec } from '../../utils/routing.js';
@@ -24,12 +25,10 @@ export async function respond(request, options, state) {
 	let url = new URL(request.url);
 
 	if (options.csrf.check_origin) {
-		const type = request.headers.get('content-type')?.split(';')[0];
-
 		const forbidden =
 			request.method === 'POST' &&
 			request.headers.get('origin') !== url.origin &&
-			(type === 'application/x-www-form-urlencoded' || type === 'multipart/form-data');
+			is_form_content_type(request);
 
 		if (forbidden) {
 			return new Response(`Cross-site ${request.method} form submissions are forbidden`, {
diff --git a/packages/kit/src/runtime/server/page/actions.js b/packages/kit/src/runtime/server/page/actions.js
index 6f9507e87279..02c038d5e814 100644
--- a/packages/kit/src/runtime/server/page/actions.js
+++ b/packages/kit/src/runtime/server/page/actions.js
@@ -1,6 +1,6 @@
 import { error, json } from '../../../exports/index.js';
 import { normalize_error } from '../../../utils/error.js';
-import { negotiate } from '../../../utils/http.js';
+import { is_form_content_type, negotiate } from '../../../utils/http.js';
 import { HttpError, Redirect, ValidationError } from '../../control.js';
 import { handle_error_and_jsonify } from '../utils.js';
 
@@ -180,9 +180,10 @@ export async function call_action(event, actions) {
 		throw new Error(`No action with name '${name}' found`);
 	}
 
-	const type = event.request.headers.get('content-type')?.split('; ')[0];
-	if (type !== 'application/x-www-form-urlencoded' && type !== 'multipart/form-data') {
-		throw new Error(`Actions expect form-encoded data (received ${type})`);
+	if (!is_form_content_type(event.request)) {
+		throw new Error(
+			`Actions expect form-encoded data (received ${event.request.headers.get('content-type')}`
+		);
 	}
 
 	return action(event);
diff --git a/packages/kit/src/utils/http.js b/packages/kit/src/utils/http.js
index 434a0f1f869f..31721d10cc4a 100644
--- a/packages/kit/src/utils/http.js
+++ b/packages/kit/src/utils/http.js
@@ -53,3 +53,20 @@ export function negotiate(accept, types) {
 
 	return accepted;
 }
+
+/**
+ * Returns `true` if the request contains a `content-type` header with the given type
+ * @param {Request} request
+ * @param  {...string} types
+ */
+export function is_content_type(request, ...types) {
+	const type = request.headers.get('content-type')?.split(';', 1)[0].trim() ?? '';
+	return types.includes(type);
+}
+
+/**
+ * @param {Request} request
+ */
+export function is_form_content_type(request) {
+	return is_content_type(request, 'application/x-www-form-urlencoded', 'multipart/form-data');
+}
diff --git a/packages/kit/test/apps/basics/src/routes/actions/success-data/+page.svelte b/packages/kit/test/apps/basics/src/routes/actions/success-data/+page.svelte
index e3699100eeba..e784d2b206b0 100644
--- a/packages/kit/test/apps/basics/src/routes/actions/success-data/+page.svelte
+++ b/packages/kit/test/apps/basics/src/routes/actions/success-data/+page.svelte
@@ -2,10 +2,12 @@
 	/** @type {import('./$types').ActionData} */
 	export let form;
 
-	async function submit() {
+	async function submit({ submitter }) {
 		const res = await fetch(this.action, {
 			method: 'POST',
-			body: new FormData(this),
+			body: submitter.getAttribute('formenctype') === 'multipart/form-data'
+				? new FormData(this)
+				: new URLSearchParams({ username: this['username'].value }),
 			headers: {
 				accept: 'application/json'
 			}
@@ -19,5 +21,6 @@
 
 <form method="post" on:submit|preventDefault={submit}>
 	<input name="username" type="text" />
-	<button>Submit</button>
+	<button formenctype="multipart/form-data">Submit</button>
+	<button formenctype="application/x-www-form-urlencoded">Submit</button>
 </form>
diff --git a/packages/kit/test/apps/basics/test/test.js b/packages/kit/test/apps/basics/test/test.js
index 93816939bd17..4522ee30b63f 100644
--- a/packages/kit/test/apps/basics/test/test.js
+++ b/packages/kit/test/apps/basics/test/test.js
@@ -1773,7 +1773,7 @@ test.describe('Actions', () => {
 		}
 	});
 
-	test('Success data is returned', async ({ page }) => {
+	test('Success data as form-data is returned', async ({ page }) => {
 		await page.goto('/actions/success-data');
 
 		expect(await page.textContent('pre')).toBe(JSON.stringify(null));
@@ -1781,12 +1781,26 @@ test.describe('Actions', () => {
 		await page.type('input[name="username"]', 'foo');
 		await Promise.all([
 			page.waitForRequest((request) => request.url().includes('/actions/success-data')),
-			page.click('button')
+			page.click('button[formenctype="multipart/form-data"]')
 		]);
 
 		await expect(page.locator('pre')).toHaveText(JSON.stringify({ result: 'foo' }));
 	});
 
+	test('Success data as form-urlencoded is returned', async ({ page }) => {
+		await page.goto('/actions/success-data');
+
+		expect(await page.textContent('pre')).toBe(JSON.stringify(null));
+
+		await page.type('input[name="username"]', 'bar');
+		await Promise.all([
+			page.waitForRequest((request) => request.url().includes('/actions/success-data')),
+			page.click('button[formenctype="application/x-www-form-urlencoded"]')
+		]);
+
+		await expect(page.locator('pre')).toHaveText(JSON.stringify({ result: 'bar' }));
+	});
+
 	test('applyAction updates form prop', async ({ page, javaScriptEnabled }) => {
 		await page.goto('/actions/update-form');
 		expect(await page.textContent('pre')).toBe(JSON.stringify(null));