diff --git a/docs/config/server-options.md b/docs/config/server-options.md
index da75fc3a46a04a..89287fe53cf98a 100644
--- a/docs/config/server-options.md
+++ b/docs/config/server-options.md
@@ -242,7 +242,7 @@ createServer()
 
 - **Type:** `string | undefined`
 
-Prepend this folder to http requests, for use when proxying vite as a subfolder. Should start and end with the `/` character.
+Prepend this folder to http requests, for use when proxying vite as a subfolder. Should start with the `/` character.
 
 ## server.fs.strict
 
diff --git a/packages/vite/src/node/build.ts b/packages/vite/src/node/build.ts
index 72b5948ccc04af..8ebe96ccd41a52 100644
--- a/packages/vite/src/node/build.ts
+++ b/packages/vite/src/node/build.ts
@@ -1138,7 +1138,7 @@ export function toOutputFilePathWithoutRuntime(
   if (relative && !config.build.ssr) {
     return toRelative(filename, hostId)
   } else {
-    return config.base + filename
+    return joinUrlSegments(config.base, filename)
   }
 }
 
diff --git a/packages/vite/src/node/config.ts b/packages/vite/src/node/config.ts
index f5cba176f5c246..5bfdea72654678 100644
--- a/packages/vite/src/node/config.ts
+++ b/packages/vite/src/node/config.ts
@@ -323,6 +323,8 @@ export type ResolvedConfig = Readonly<
     inlineConfig: InlineConfig
     root: string
     base: string
+    /** @internal */
+    rawBase: string
     publicDir: string
     cacheDir: string
     command: 'build' | 'serve'
@@ -626,7 +628,8 @@ export async function resolveConfig(
     ),
     inlineConfig,
     root: resolvedRoot,
-    base: resolvedBase,
+    base: resolvedBase.endsWith('/') ? resolvedBase : resolvedBase + '/',
+    rawBase: resolvedBase,
     resolve: resolveOptions,
     publicDir: resolvedPublicDir,
     cacheDir,
@@ -819,12 +822,6 @@ export function resolveBaseUrl(
       colors.yellow(colors.bold(`(!) "base" option should start with a slash.`))
     )
   }
-  // no ending slash warn
-  if (!base.endsWith('/')) {
-    logger.warn(
-      colors.yellow(colors.bold(`(!) "base" option should end with a slash.`))
-    )
-  }
 
   // parse base when command is serve or base is not External URL
   if (!isBuild || !isExternal) {
@@ -834,10 +831,6 @@ export function resolveBaseUrl(
       base = '/' + base
     }
   }
-  // ensure ending slash
-  if (!base.endsWith('/')) {
-    base += '/'
-  }
 
   return base
 }
diff --git a/packages/vite/src/node/plugins/asset.ts b/packages/vite/src/node/plugins/asset.ts
index 9bb5d7f7a42d84..0d67af4fa0e05b 100644
--- a/packages/vite/src/node/plugins/asset.ts
+++ b/packages/vite/src/node/plugins/asset.ts
@@ -247,7 +247,7 @@ function fileToDevUrl(id: string, config: ResolvedConfig) {
   } else {
     // outside of project root, use absolute fs path
     // (this is special handled by the serve static middleware
-    rtn = path.posix.join(FS_PREFIX + id)
+    rtn = path.posix.join(FS_PREFIX, id)
   }
   const base = joinUrlSegments(config.server?.origin ?? '', config.base)
   return joinUrlSegments(base, rtn.replace(/^\//, ''))
diff --git a/packages/vite/src/node/plugins/css.ts b/packages/vite/src/node/plugins/css.ts
index c14269ccf99734..caa7a36f80cbeb 100644
--- a/packages/vite/src/node/plugins/css.ts
+++ b/packages/vite/src/node/plugins/css.ts
@@ -46,6 +46,7 @@ import {
   processSrcSet,
   removeDirectQuery,
   requireResolveFromRootWithFallback,
+  stripBase,
   stripBomTag
 } from '../utils'
 import type { Logger } from '../logger'
@@ -265,9 +266,10 @@ export function cssPlugin(config: ResolvedConfig): Plugin {
                 isCSSRequest(file)
                   ? moduleGraph.createFileOnlyEntry(file)
                   : await moduleGraph.ensureEntryFromUrl(
-                      (
-                        await fileToUrl(file, config, this)
-                      ).replace((config.server?.origin ?? '') + devBase, '/'),
+                      stripBase(
+                        await fileToUrl(file, config, this),
+                        (config.server?.origin ?? '') + devBase
+                      ),
                       ssr
                     )
               )
diff --git a/packages/vite/src/node/plugins/importAnalysis.ts b/packages/vite/src/node/plugins/importAnalysis.ts
index 80ee54e501a26e..d15496d6d34c17 100644
--- a/packages/vite/src/node/plugins/importAnalysis.ts
+++ b/packages/vite/src/node/plugins/importAnalysis.ts
@@ -33,10 +33,12 @@ import {
   isDataUrl,
   isExternalUrl,
   isJSRequest,
+  joinUrlSegments,
   moduleListContains,
   normalizePath,
   prettifyUrl,
   removeImportQuery,
+  stripBase,
   stripBomTag,
   timeFrom,
   transformStableResult,
@@ -263,9 +265,7 @@ export function importAnalysisPlugin(config: ResolvedConfig): Plugin {
         url: string,
         pos: number
       ): Promise<[string, string]> => {
-        if (base !== '/' && url.startsWith(base)) {
-          url = url.replace(base, '/')
-        }
+        url = stripBase(url, base)
 
         let importerFile = importer
 
@@ -319,7 +319,7 @@ export function importAnalysisPlugin(config: ResolvedConfig): Plugin {
         ) {
           // an optimized deps may not yet exists in the filesystem, or
           // a regular file exists but is out of root: rewrite to absolute /@fs/ paths
-          url = path.posix.join(FS_PREFIX + resolved.id)
+          url = path.posix.join(FS_PREFIX, resolved.id)
         } else {
           url = resolved.id
         }
@@ -376,8 +376,8 @@ export function importAnalysisPlugin(config: ResolvedConfig): Plugin {
             throw e
           }
 
-          // prepend base (dev base is guaranteed to have ending slash)
-          url = base + url.replace(/^\//, '')
+          // prepend base
+          url = joinUrlSegments(base, url)
         }
 
         return [url, resolved.id]
@@ -538,7 +538,7 @@ export function importAnalysisPlugin(config: ResolvedConfig): Plugin {
 
           // record for HMR import chain analysis
           // make sure to unwrap and normalize away base
-          const hmrUrl = unwrapId(url.replace(base, '/'))
+          const hmrUrl = unwrapId(stripBase(url, base))
           importedUrls.add(hmrUrl)
 
           if (enablePartialAccept && importedBindings) {
diff --git a/packages/vite/src/node/server/middlewares/base.ts b/packages/vite/src/node/server/middlewares/base.ts
index 93d7b4950323d9..08aa76577a7a6f 100644
--- a/packages/vite/src/node/server/middlewares/base.ts
+++ b/packages/vite/src/node/server/middlewares/base.ts
@@ -1,24 +1,23 @@
 import type { Connect } from 'dep-types/connect'
 import type { ViteDevServer } from '..'
-import { joinUrlSegments } from '../../utils'
+import { joinUrlSegments, stripBase } from '../../utils'
 
-// this middleware is only active when (config.base !== '/')
+// this middleware is only active when (base !== '/')
 
 export function baseMiddleware({
   config
 }: ViteDevServer): Connect.NextHandleFunction {
-  const devBase = config.base.endsWith('/') ? config.base : config.base + '/'
-
   // Keep the named function. The name is visible in debug logs via `DEBUG=connect:dispatcher ...`
   return function viteBaseMiddleware(req, res, next) {
     const url = req.url!
     const parsed = new URL(url, 'http://vitejs.dev')
     const path = parsed.pathname || '/'
+    const base = config.rawBase
 
-    if (path.startsWith(devBase)) {
+    if (path.startsWith(base)) {
       // rewrite url to remove base. this ensures that other middleware does
       // not need to consider base being prepended or not
-      req.url = url.replace(devBase, '/')
+      req.url = stripBase(url, base)
       return next()
     }
 
@@ -30,18 +29,19 @@ export function baseMiddleware({
     if (path === '/' || path === '/index.html') {
       // redirect root visit to based url with search and hash
       res.writeHead(302, {
-        Location: config.base + (parsed.search || '') + (parsed.hash || '')
+        Location: base + (parsed.search || '') + (parsed.hash || '')
       })
       res.end()
       return
     } else if (req.headers.accept?.includes('text/html')) {
       // non-based page visit
-      const redirectPath = joinUrlSegments(config.base, url)
+      const redirectPath =
+        url + '/' !== base ? joinUrlSegments(base, url) : base
       res.writeHead(404, {
         'Content-Type': 'text/html'
       })
       res.end(
-        `The server is configured with a public base URL of ${config.base} - ` +
+        `The server is configured with a public base URL of ${base} - ` +
           `did you mean to visit <a href="${redirectPath}">${redirectPath}</a> instead?`
       )
       return
diff --git a/packages/vite/src/node/utils.ts b/packages/vite/src/node/utils.ts
index 3c1e9c90f2a034..379e633e14591a 100644
--- a/packages/vite/src/node/utils.ts
+++ b/packages/vite/src/node/utils.ts
@@ -868,7 +868,8 @@ export async function resolveServerUrls(
   const hostname = await resolveHostname(options.host)
   const protocol = options.https ? 'https' : 'http'
   const port = address.port
-  const base = config.base === './' || config.base === '' ? '/' : config.base
+  const base =
+    config.rawBase === './' || config.rawBase === '' ? '/' : config.rawBase
 
   if (hostname.host && loopbackHosts.has(hostname.host)) {
     let hostnameName = hostname.name
@@ -1250,6 +1251,14 @@ export function joinUrlSegments(a: string, b: string): string {
   return a + b
 }
 
+export function stripBase(path: string, base: string): string {
+  if (path === base) {
+    return '/'
+  }
+  const devBase = base.endsWith('/') ? base : base + '/'
+  return path.replace(RegExp('^' + devBase), '/')
+}
+
 export function arrayEqual(a: any[], b: any[]): boolean {
   if (a === b) return true
   if (a.length !== b.length) return false
diff --git a/playground/assets/__tests__/assets.spec.ts b/playground/assets/__tests__/assets.spec.ts
index f8246a4f3418b3..3c20dc96246574 100644
--- a/playground/assets/__tests__/assets.spec.ts
+++ b/playground/assets/__tests__/assets.spec.ts
@@ -1,3 +1,4 @@
+import path from 'node:path'
 import fetch from 'node-fetch'
 import { describe, expect, test } from 'vitest'
 import {
@@ -30,8 +31,12 @@ test('should have no 404s', () => {
 })
 
 test('should get a 404 when using incorrect case', async () => {
-  expect((await fetch(viteTestUrl + 'icon.png')).status).toBe(200)
-  expect((await fetch(viteTestUrl + 'ICON.png')).status).toBe(404)
+  expect((await fetch(path.posix.join(viteTestUrl, 'icon.png'))).status).toBe(
+    200
+  )
+  expect((await fetch(path.posix.join(viteTestUrl, 'ICON.png'))).status).toBe(
+    404
+  )
 })
 
 describe('injected scripts', () => {
@@ -312,7 +317,7 @@ test('new URL(`${dynamic}`, import.meta.url)', async () => {
 
 test('new URL(`non-existent`, import.meta.url)', async () => {
   expect(await page.textContent('.non-existent-import-meta-url')).toMatch(
-    '/foo/non-existent'
+    new URL('non-existent', page.url()).pathname
   )
 })
 
diff --git a/playground/assets/package.json b/playground/assets/package.json
index d3b685dbed678b..6d28ed91719070 100644
--- a/playground/assets/package.json
+++ b/playground/assets/package.json
@@ -3,9 +3,9 @@
   "private": true,
   "version": "0.0.0",
   "scripts": {
+    "debug": "node --inspect-brk ../../packages/vite/bin/vite",
     "dev": "vite",
     "build": "vite build",
-    "debug": "node --inspect-brk ../../packages/vite/bin/vite",
     "preview": "vite preview",
     "dev:relative-base": "vite --config ./vite.config-relative-base.js dev",
     "build:relative-base": "vite --config ./vite.config-relative-base.js build",
diff --git a/playground/assets/vite.config.js b/playground/assets/vite.config.js
index 700896cc13d50b..ff4789679659d8 100644
--- a/playground/assets/vite.config.js
+++ b/playground/assets/vite.config.js
@@ -4,7 +4,7 @@ const path = require('node:path')
  * @type {import('vite').UserConfig}
  */
 module.exports = {
-  base: '/foo/',
+  base: '/foo',
   publicDir: 'static',
   resolve: {
     alias: {