diff --git a/.changeset/twenty-cherries-switch.md b/.changeset/twenty-cherries-switch.md
new file mode 100644
index 0000000000000..c79c53284e213
--- /dev/null
+++ b/.changeset/twenty-cherries-switch.md
@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fixes a bug that caused the dev server to return an error if requesting "//"
diff --git a/packages/astro/src/core/routing/manifest/create.ts b/packages/astro/src/core/routing/manifest/create.ts
index 6dbcf18aee687..1b7d30f9cd3e0 100644
--- a/packages/astro/src/core/routing/manifest/create.ts
+++ b/packages/astro/src/core/routing/manifest/create.ts
@@ -427,6 +427,10 @@ function detectRouteCollision(a: RouteData, b: RouteData, _config: AstroConfig,
 		// Fallbacks are always added below other routes exactly to avoid collisions.
 		return;
 	}
+	// The double-slash redirect will never collide with any other route.
+	if (a.route === '//' || b.route === '//') {
+		return;
+	}
 
 	if (
 		a.route === b.route &&
@@ -502,6 +506,27 @@ export async function createRouteManifest(
 	}
 
 	const redirectRoutes = createRedirectRoutes(params, routeMap, logger);
+	if (dev) {
+		// Add a redirect for `//` to `/`. We only do this in dev because different platforms
+		// vary a lot in how or whether they handle this sort of redirect, so we leave it to the adapter
+		redirectRoutes.push({
+			type: 'redirect',
+			isIndex: false,
+			route: '//',
+			pattern: /^\/+$/,
+			segments: [],
+			params: [],
+			component: '/',
+			generate: () => '//',
+			pathname: '//',
+			prerender: false,
+			redirect: '/',
+			redirectRoute: routeMap.get('/'),
+			fallbackRoutes: [],
+			distURL: [],
+			origin: 'project',
+		});
+	}
 
 	// we remove the file based routes that were deemed redirects
 	const filteredFiledBasedRoutes = fileBasedRoutes.filter((fileBasedRoute) => {
diff --git a/packages/astro/src/vite-plugin-astro-server/base.ts b/packages/astro/src/vite-plugin-astro-server/base.ts
index 562b89ba22040..89fc13805f480 100644
--- a/packages/astro/src/vite-plugin-astro-server/base.ts
+++ b/packages/astro/src/vite-plugin-astro-server/base.ts
@@ -9,6 +9,8 @@ import type { Logger } from '../core/logger/core.js';
 import notFoundTemplate, { subpathNotUsedTemplate } from '../template/4xx.js';
 import { writeHtmlResponse } from './response.js';
 
+const justSlashes = /^\/{2,}$/;
+
 export function baseMiddleware(
 	settings: AstroSettings,
 	logger: Logger,
@@ -24,7 +26,7 @@ export function baseMiddleware(
 
 		let pathname: string;
 		try {
-			pathname = decodeURI(new URL(url, 'http://localhost').pathname);
+			pathname = justSlashes.test(url) ? '//' : decodeURI(new URL(url, 'http://localhost').pathname);
 		} catch (e) {
 			/* malform uri */
 			return next(e);
diff --git a/packages/astro/test/dev-routing.test.js b/packages/astro/test/dev-routing.test.js
index c6a19fc4e4408..a43561769a1a6 100644
--- a/packages/astro/test/dev-routing.test.js
+++ b/packages/astro/test/dev-routing.test.js
@@ -48,6 +48,19 @@ describe('Development Routing', () => {
 			assert.equal(response.status, 200);
 		});
 
+		it('redirects when loading double slash', async () => {
+			const response = await fixture.fetch('//', { redirect: 'manual' });
+			assert.equal(response.status, 301);
+			assert.equal(response.headers.get('Location'), '/');
+		});
+
+		it('redirects when loading multiple slashes', async () => {
+			const response = await fixture.fetch('/////', { redirect: 'manual' });
+			assert.equal(response.status, 301);
+			assert.equal(response.headers.get('Location'), '/');
+		});
+
+
 		it('404 when loading invalid dynamic route', async () => {
 			const response = await fixture.fetch('/2');
 			assert.equal(response.status, 404);