8 files changed, 45 insertions, 9 deletions
diff --git a/.changeset/happy-carrots-lick.md b/.changeset/happy-carrots-lick.md
new file mode 100644
index 000000000..7dcd38568
--- /dev/null
+++ b/.changeset/happy-carrots-lick.md
@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fix `status` code for custom `404` and `500` pages in the dev server
diff --git a/packages/astro/src/vite-plugin-astro-server/route.ts b/packages/astro/src/vite-plugin-astro-server/route.ts
index 8b8bf3482..d7b8c9a9e 100644
--- a/packages/astro/src/vite-plugin-astro-server/route.ts
+++ b/packages/astro/src/vite-plugin-astro-server/route.ts
@@ -25,7 +25,7 @@ type AsyncReturnType<T extends (...args: any) => Promise<any>> = T extends (
 	? R
 	: any;
 
-interface MatchedRoute {
+export interface MatchedRoute {
 	route: RouteData;
 	filePath: URL;
 	resolvedPathname: string;
@@ -125,12 +125,14 @@ type HandleRoute = {
 	incomingRequest: http.IncomingMessage;
 	incomingResponse: http.ServerResponse;
 	manifest: SSRManifest;
+	status?: number;
 };
 
 export async function handleRoute({
 	matchedRoute,
 	url,
 	pathname,
+	status = getStatus(matchedRoute),
 	body,
 	origin,
 	env,
@@ -198,6 +200,7 @@ export async function handleRoute({
 					matchedRoute: fourOhFourRoute,
 					url: new URL('/404', url),
 					pathname: '/404',
+					status: 404,
 					body,
 					origin,
 					env,
@@ -236,6 +239,7 @@ export async function handleRoute({
 				...options,
 				matchedRoute: fourOhFourRoute,
 				url: new URL(pathname, url),
+				status: 404,
 				body,
 				origin,
 				env,
@@ -246,6 +250,18 @@ export async function handleRoute({
 			});
 		}
 		throwIfRedirectNotAllowed(result, config);
-		return await writeSSRResult(request, result, incomingResponse);
+
+		let response = result;
+		// Response.status is read-only, so a clone is required to override
+		if (status && response.status !== status) {
+			response = new Response(result.body, { ...result, status });
+		}
+		return await writeSSRResult(request, response, incomingResponse);
 	}
 }
+
+function getStatus(matchedRoute?: MatchedRoute): number | undefined {
+	if (!matchedRoute) return 404;
+	if (matchedRoute.route.route === '/404') return 404;
+	if (matchedRoute.route.route === '/500') return 500;
+}
diff --git a/packages/astro/test/custom-404-html.test.js b/packages/astro/test/custom-404-html.test.js
index 6c3ac6dec..56d595165 100644
--- a/packages/astro/test/custom-404-html.test.js
+++ b/packages/astro/test/custom-404-html.test.js
@@ -32,7 +32,10 @@ describe('Custom 404.html', () => {
 		});
 
 		it('renders 404 for /a', async () => {
-			const html = await fixture.fetch('/a').then((res) => res.text());
+			const res = await fixture.fetch('/a');
+			expect(res.status).to.equal(404);
+
+			const html = await res.text();
 			$ = cheerio.load(html);
 
 			expect($('h1').text()).to.equal('Page not found');
diff --git a/packages/astro/test/custom-404-injected.test.js b/packages/astro/test/custom-404-injected.test.js
index c8963243a..7940bde88 100644
--- a/packages/astro/test/custom-404-injected.test.js
+++ b/packages/astro/test/custom-404-injected.test.js
@@ -32,7 +32,10 @@ describe('Custom 404 with injectRoute', () => {
 		});
 
 		it('renders 404 for /a', async () => {
-			const html = await fixture.fetch('/a').then((res) => res.text());
+			const res = await fixture.fetch('/a');
+			expect(res.status).to.equal(404);
+
+			const html = await res.text();
 			$ = cheerio.load(html);
 
 			expect($('h1').text()).to.equal('Page not found');
diff --git a/packages/astro/test/custom-404-md.test.js b/packages/astro/test/custom-404-md.test.js
index 69eddb26b..a7762004f 100644
--- a/packages/astro/test/custom-404-md.test.js
+++ b/packages/astro/test/custom-404-md.test.js
@@ -31,7 +31,10 @@ describe('Custom 404 Markdown', () => {
 		});
 
 		it('renders 404 for /abc', async () => {
-			const html = await fixture.fetch('/a').then((res) => res.text());
+			const res = await fixture.fetch('/a');
+			expect(res.status).to.equal(404);
+
+			const html = await res.text();
 			$ = cheerio.load(html);
 
 			expect($('h1').text()).to.equal('Page not found');
diff --git a/packages/astro/test/custom-404-server.test.js b/packages/astro/test/custom-404-server.test.js
index db09bfbab..0c824546b 100644
--- a/packages/astro/test/custom-404-server.test.js
+++ b/packages/astro/test/custom-404-server.test.js
@@ -32,7 +32,10 @@ describe('Custom 404 server', () => {
 		});
 
 		it('renders 404 for /a', async () => {
-			const html = await fixture.fetch('/a').then((res) => res.text());
+			const res = await fixture.fetch('/a');
+			expect(res.status).to.equal(404);
+
+			const html = await res.text();
 			$ = cheerio.load(html);
 
 			expect($('h1').text()).to.equal('Page not found');
diff --git a/packages/astro/test/custom-404.test.js b/packages/astro/test/custom-404.test.js
index a3294d9b1..c744f124c 100644
--- a/packages/astro/test/custom-404.test.js
+++ b/packages/astro/test/custom-404.test.js
@@ -32,7 +32,10 @@ describe('Custom 404', () => {
 		});
 
 		it('renders 404 for /a', async () => {
-			const html = await fixture.fetch('/a').then((res) => res.text());
+			const res = await fixture.fetch('/a');
+			expect(res.status).to.equal(404);
+
+			const html = await res.text();
 			$ = cheerio.load(html);
 
 			expect($('h1').text()).to.equal('Page not found');
diff --git a/packages/astro/test/units/dev/dev.test.js b/packages/astro/test/units/dev/dev.test.js
index 5c19af635..7c361b9de 100644
--- a/packages/astro/test/units/dev/dev.test.js
+++ b/packages/astro/test/units/dev/dev.test.js
@@ -205,7 +205,7 @@ describe('dev container', () => {
 					await r.done;
 					const doc = await r.text();
 					expect(doc).to.match(/<h1>Custom 404<\/h1>/);
-					expect(r.res.statusCode).to.equal(200);
+					expect(r.res.statusCode).to.equal(404);
 				}
 				{
 					// A non-existent page also serves the custom 404 page.
@@ -214,7 +214,7 @@ describe('dev container', () => {
 					await r.done;
 					const doc = await r.text();
 					expect(doc).to.match(/<h1>Custom 404<\/h1>/);
-					expect(r.res.statusCode).to.equal(200);
+					expect(r.res.statusCode).to.equal(404);
 				}
 			}
 		);