diff --git a/packages/plugin-rsc/src/plugin.ts b/packages/plugin-rsc/src/plugin.ts
index f5c9c8f29..27f4a40e4 100644
--- a/packages/plugin-rsc/src/plugin.ts
+++ b/packages/plugin-rsc/src/plugin.ts
@@ -66,6 +66,7 @@ import {
   directRequestRE,
   evalValue,
   normalizeViteImportAnalysisUrl,
+  parseRequestUrl,
   prepareError,
   slash,
 } from './plugins/vite-utils'
@@ -1056,7 +1057,11 @@ export default function vitePluginRsc(
         }
 
         server.middlewares.use(async (req, res, next) => {
-          const url = new URL(req.url ?? '/', `http://localhost`)
+          const url = parseRequestUrl(req.url)
+          if (!url) {
+            next()
+            return
+          }
           if (url.pathname === '/__vite_rsc_load_module_dev_proxy') {
             try {
               const handler = await createHandler(url)
diff --git a/packages/plugin-rsc/src/plugins/find-source-map-url.ts b/packages/plugin-rsc/src/plugins/find-source-map-url.ts
index 4f84bc63c..fa77bff26 100644
--- a/packages/plugin-rsc/src/plugins/find-source-map-url.ts
+++ b/packages/plugin-rsc/src/plugins/find-source-map-url.ts
@@ -6,7 +6,7 @@ import {
   type Plugin,
   type ViteDevServer,
 } from 'vite'
-import { slash } from './vite-utils'
+import { parseRequestUrl, slash } from './vite-utils'
 
 //
 // support findSourceMapURL
@@ -21,7 +21,11 @@ export function vitePluginFindSourceMapURL(): Plugin[] {
       apply: 'serve',
       configureServer(server) {
         server.middlewares.use(async (req, res, next) => {
-          const url = new URL(req.url!, `http://localhost`)
+          const url = parseRequestUrl(req.url)
+          if (!url) {
+            next()
+            return
+          }
           if (url.pathname === '/__vite_rsc_findSourceMapURL') {
             let filename = url.searchParams.get('filename')!
             let environmentName = url.searchParams.get('environmentName')!
diff --git a/packages/plugin-rsc/src/plugins/vite-utils.test.ts b/packages/plugin-rsc/src/plugins/vite-utils.test.ts
new file mode 100644
index 000000000..133243a72
--- /dev/null
+++ b/packages/plugin-rsc/src/plugins/vite-utils.test.ts
@@ -0,0 +1,21 @@
+import { describe, expect, it } from 'vitest'
+import { parseRequestUrl } from './vite-utils'
+
+describe(parseRequestUrl, () => {
+  it('parses normal request urls', () => {
+    expect(parseRequestUrl('/')?.pathname).toBe('/')
+    expect(
+      parseRequestUrl('/__vite_rsc_findSourceMapURL?filename=a')?.pathname,
+    ).toBe('/__vite_rsc_findSourceMapURL')
+    expect(parseRequestUrl(undefined)?.pathname).toBe('/')
+  })
+
+  it('returns undefined instead of throwing for unparseable request urls', () => {
+    // A request to `//` is valid HTTP but `new URL('//', base)` throws
+    // ERR_INVALID_URL. An uncaught throw inside an async Connect middleware
+    // becomes an unhandled rejection and kills the dev server, so the
+    // middleware skips to `next()` on undefined instead.
+    expect(parseRequestUrl('//')).toBeUndefined()
+    expect(parseRequestUrl('//[')).toBeUndefined()
+  })
+})
diff --git a/packages/plugin-rsc/src/plugins/vite-utils.ts b/packages/plugin-rsc/src/plugins/vite-utils.ts
index 1ebe38372..a5e11e060 100644
--- a/packages/plugin-rsc/src/plugins/vite-utils.ts
+++ b/packages/plugin-rsc/src/plugins/vite-utils.ts
@@ -165,3 +165,15 @@ export function evalValue<T = any>(rawValue: string): T {
 
 // https://github.com/vitejs/vite/blob/84079a84ad94de4c1ef4f1bdb2ab448ff2c01196/packages/vite/src/node/utils.ts#L321
 export const directRequestRE: RegExp = /(\?|&)direct=?(?:&|$)/
+
+// Parse an incoming dev-middleware request URL without throwing. Requests
+// like `//` or `//[` are valid HTTP but do not parse as URLs; an uncaught
+// throw inside an async Connect middleware becomes an unhandled rejection
+// and takes down the whole dev server. Callers skip to `next()` on undefined.
+export function parseRequestUrl(reqUrl: string | undefined): URL | undefined {
+  try {
+    return new URL(reqUrl ?? '/', 'http://localhost')
+  } catch {
+    return undefined
+  }
+}