diff --git a/.changeset/fix-set-cookie-304.md b/.changeset/fix-set-cookie-304.md
new file mode 100644
index 000000000000..358ae26dc01f
--- /dev/null
+++ b/.changeset/fix-set-cookie-304.md
@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: preserve multiple `Set-Cookie` headers on 304 responses
diff --git a/packages/kit/src/runtime/server/respond.js b/packages/kit/src/runtime/server/respond.js
index 6a7395b40b44..38e31e38376a 100644
--- a/packages/kit/src/runtime/server/respond.js
+++ b/packages/kit/src/runtime/server/respond.js
@@ -511,19 +511,18 @@ export async function internal_respond(request, options, manifest, state) {
 			if (if_none_match_value === etag) {
 				const headers = new Headers({ etag });
 
-				// https://datatracker.ietf.org/doc/html/rfc7232#section-4.1 + set-cookie
-				for (const key of [
-					'cache-control',
-					'content-location',
-					'date',
-					'expires',
-					'vary',
-					'set-cookie'
-				]) {
+				// https://datatracker.ietf.org/doc/html/rfc7232#section-4.1
+				for (const key of ['cache-control', 'content-location', 'date', 'expires', 'vary']) {
 					const value = response.headers.get(key);
 					if (value) headers.set(key, value);
 				}
 
+				// `Headers.get('set-cookie')` collapses multiple values into a single
+				// comma-joined string that browsers cannot parse correctly
+				for (const cookie of response.headers.getSetCookie()) {
+					headers.append('set-cookie', cookie);
+				}
+
 				return new Response(undefined, {
 					status: 304,
 					headers
diff --git a/packages/kit/test/apps/basics/src/routes/cookies/forwarded-in-etag-multiple/+page.server.js b/packages/kit/test/apps/basics/src/routes/cookies/forwarded-in-etag-multiple/+page.server.js
new file mode 100644
index 000000000000..eaa867774f12
--- /dev/null
+++ b/packages/kit/test/apps/basics/src/routes/cookies/forwarded-in-etag-multiple/+page.server.js
@@ -0,0 +1,6 @@
+/** @type {import('./$types').PageServerLoad} */
+export function load({ cookies }) {
+	cookies.set('one', '1', { path: '', httpOnly: false });
+	cookies.set('two', '2', { path: '', httpOnly: false });
+	cookies.set('three', '3', { path: '', httpOnly: false });
+}
diff --git a/packages/kit/test/apps/basics/src/routes/cookies/forwarded-in-etag-multiple/+page.svelte b/packages/kit/test/apps/basics/src/routes/cookies/forwarded-in-etag-multiple/+page.svelte
new file mode 100644
index 000000000000..63892ef9685b
--- /dev/null
+++ b/packages/kit/test/apps/basics/src/routes/cookies/forwarded-in-etag-multiple/+page.svelte
@@ -0,0 +1,27 @@
+<script>
+	import { onMount } from 'svelte';
+
+	/** @type {string} */
+	let cookies;
+
+	onMount(() => {
+		cookies = document.cookie
+			.split('; ')
+			.filter((c) => c.startsWith('one=') || c.startsWith('two=') || c.startsWith('three='))
+			.sort()
+			.join('; ');
+	});
+</script>
+
+<button
+	on:click={() => {
+		for (const name of ['one', 'two', 'three']) {
+			document.cookie = `${name}=;expires=Thu, 01 Jan 1970 00:00:01 GMT;`;
+		}
+		location.reload();
+	}}
+>
+	Delete cookies and reload the page
+</button>
+
+<p>{cookies}</p>
diff --git a/packages/kit/test/apps/basics/test/cross-platform/client.test.js b/packages/kit/test/apps/basics/test/cross-platform/client.test.js
index 3a9322c1560f..3d888b74113e 100644
--- a/packages/kit/test/apps/basics/test/cross-platform/client.test.js
+++ b/packages/kit/test/apps/basics/test/cross-platform/client.test.js
@@ -1188,6 +1188,13 @@ test.describe('cookies', () => {
 		await expect(page.locator('p')).toHaveText('foo=bar');
 	});
 
+	test('etag forwards multiple cookies', async ({ page }) => {
+		await page.goto('/cookies/forwarded-in-etag-multiple');
+		await expect(page.locator('p')).toHaveText('one=1; three=3; two=2');
+		await page.locator('button').click();
+		await expect(page.locator('p')).toHaveText('one=1; three=3; two=2');
+	});
+
 	test("fetch during SSR doesn't un- and re-escape cookies", async ({ page }) => {
 		await page.goto('/cookies/collect-without-re-escaping');
 		await expect(page.locator('p')).toHaveText('cookie-special-characters="foo"');