withastro · ascorbic · Jul 18, 2025 · Jul 15, 2025 · Jul 15, 2025 · Jul 15, 2025
diff --git a/.changeset/lucky-cameras-notice.md b/.changeset/lucky-cameras-notice.md
@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fixes an issue where Astro's default 404 route would incorrectly match routes containing "/404" in dev
diff --git a/packages/astro/src/core/routing/astro-designed-error-pages.ts b/packages/astro/src/core/routing/astro-designed-error-pages.ts
@@ -7,7 +7,7 @@ export const DEFAULT_404_ROUTE: RouteData = {
 	component: DEFAULT_404_COMPONENT,
 	generate: () => '',
 	params: [],
-	pattern: /\/404/,
+	pattern: /^\/404\/?$/,
 	prerender: false,
 	pathname: '/404',
 	segments: [[{ content: '404', dynamic: false, spread: false }]],

diff --git a/packages/astro/test/fixtures/user-route-priority/package.json b/packages/astro/test/fixtures/user-route-priority/package.json
@@ -0,0 +1,8 @@
+{
+  "name": "@test/user-route-priority",
+  "version": "0.0.0",
+  "private": true,
+  "dependencies": {
+    "astro": "workspace:*"
+  }
+}
diff --git a/packages/astro/test/fixtures/user-route-priority/public/favicon.ico b/packages/astro/test/fixtures/user-route-priority/public/favicon.ico
diff --git a/packages/astro/test/fixtures/user-route-priority/src/pages/[number].astro b/packages/astro/test/fixtures/user-route-priority/src/pages/[number].astro
@@ -0,0 +1,12 @@
+---
+const val = Number(Astro.params.number);
+---
+<html>
+<head>
+	<title>Test app</title>
+	<style>body { font-size: 11px; }</style>
+</head>
+<body>
+	<h1>{ val }</h1>
+</body>
+</html>
diff --git a/packages/astro/test/user-route-priority.test.js b/packages/astro/test/user-route-priority.test.js
@@ -0,0 +1,40 @@
+import assert from 'node:assert/strict';
+import { before, describe, it } from 'node:test';
+import { load as cheerioLoad } from 'cheerio';
+import testAdapter from './test-adapter.js';
+import { loadFixture } from './test-utils.js';
+
+describe('User routes have priority over internal routes', () => {
+	/** @type {import('./test-utils.js').Fixture} */
+	let fixture;
+
+	before(async () => {
+		const root = './fixtures/user-route-priority/';
+		fixture = await loadFixture({
+			root,
+			output: 'server',
+			adapter: testAdapter()
+		});
+		await fixture.build();
+	});
+
+	async function fetchHTML(path) {
+		const app = await fixture.loadTestAdapterApp();
+		const request = new Request('http://example.com' + path);
+		const response = await app.render(request);
+		const html = await response.text();
+		return html;
+	}
+
+	it("Page doesn't error with non-404 as number", async () => {
+		const html = await fetchHTML('/123');
+		const $ = cheerioLoad(html);
+		assert.equal($('h1').text(), '123');
+	});
+
+	it("Page doesn't error with 404 as number", async () => {
+		const html = await fetchHTML('/404');
+		const $ = cheerioLoad(html);
+		assert.equal($('h1').text(), '404');
+	});
+});
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml