diff --git a/.changeset/plenty-eyes-develop.md b/.changeset/plenty-eyes-develop.md
new file mode 100644
index 000000000..74073721b
--- /dev/null
+++ b/.changeset/plenty-eyes-develop.md
@@ -0,0 +1,7 @@
+---
+'astro': patch
+---
+
+404 when not using subpath for items in public in dev
+
+Previously if using a base like `base: '/subpath/` you could load things from the root, which would break in prod. Now you must include the subpath.
diff --git a/packages/astro/src/vite-plugin-astro-server/base.ts b/packages/astro/src/vite-plugin-astro-server/base.ts
index 2618749db..dcab634b7 100644
--- a/packages/astro/src/vite-plugin-astro-server/base.ts
+++ b/packages/astro/src/vite-plugin-astro-server/base.ts
@@ -5,6 +5,7 @@ import { LogOptions } from '../core/logger/core.js';
 import notFoundTemplate, { subpathNotUsedTemplate } from '../template/4xx.js';
 import { log404 } from './common.js';
 import { writeHtmlResponse } from './response.js';
+import * as fs from 'fs';
 
 export function baseMiddleware(
 	settings: AstroSettings,
@@ -12,12 +13,13 @@ export function baseMiddleware(
 ): vite.Connect.NextHandleFunction {
 	const { config } = settings;
 	const site = config.site ? new URL(config.base, config.site) : undefined;
-	const devRoot = site ? site.pathname : '/';
+	const devRoot = site ? site.pathname : new URL(config.base, 'http://localhost').pathname;
 
 	return function devBaseMiddleware(req, res, next) {
 		const url = req.url!;
 
-		const pathname = decodeURI(new URL(url, 'http://vitejs.dev').pathname);
+		const pathname = decodeURI(new URL(url, 'http://localhost').pathname);
+
 
 		if (pathname.startsWith(devRoot)) {
 			req.url = url.replace(devRoot, '/');
@@ -41,6 +43,16 @@ export function baseMiddleware(
 			return writeHtmlResponse(res, 404, html);
 		}
 
-		next();
+		// Check to see if it's in public and if so 404
+		const publicPath = new URL('.' + req.url, config.publicDir);
+		fs.stat(publicPath, (_err, stats) => {
+			if(stats) {
+				log404(logging, pathname);
+				const html = subpathNotUsedTemplate(devRoot, pathname);
+				return writeHtmlResponse(res, 404, html);
+			} else {
+				next();
+			}
+		});
 	};
 }
diff --git a/packages/astro/test/fixtures/alias/public/test.txt b/packages/astro/test/fixtures/alias/public/test.txt
new file mode 100644
index 000000000..90bfcb510
--- /dev/null
+++ b/packages/astro/test/fixtures/alias/public/test.txt
@@ -0,0 +1 @@
+this is a test
diff --git a/packages/astro/test/units/dev/dev.test.js b/packages/astro/test/units/dev/dev.test.js
index 88fbaac45..062fcba23 100644
--- a/packages/astro/test/units/dev/dev.test.js
+++ b/packages/astro/test/units/dev/dev.test.js
@@ -157,4 +157,50 @@ describe('dev container', () => {
 			}
 		);
 	});
+
+	it('items in public/ are not available from root when using a base', async () => {
+		await runInContainer({
+			root,
+			userConfig: {
+				base: '/sub/'
+			}
+		}, async (container) => {
+			// First try the subpath
+			let r = createRequestAndResponse({
+				method: 'GET',
+				url: '/sub/test.txt',
+			});
+
+			container.handle(r.req, r.res);
+			await r.done;
+
+			expect(r.res.statusCode).to.equal(200);
+
+			// Next try the root path
+			r = createRequestAndResponse({
+				method: 'GET',
+				url: '/test.txt',
+			});
+
+			container.handle(r.req, r.res);
+			await r.done;
+
+			expect(r.res.statusCode).to.equal(404);
+		});
+	});
+
+	it('items in public/ are available from root when not using a base', async () => {
+		await runInContainer({ root }, async (container) => {
+			// Try the root path
+			let r = createRequestAndResponse({
+				method: 'GET',
+				url: '/test.txt',
+			});
+
+			container.handle(r.req, r.res);
+			await r.done;
+
+			expect(r.res.statusCode).to.equal(200);
+		});
+	});
 });