diff --git a/packages/vite/src/node/server/middlewares/proxy.ts b/packages/vite/src/node/server/middlewares/proxy.ts
index 0f83ecb723fa19..9f07a3c6e7bc24 100644
--- a/packages/vite/src/node/server/middlewares/proxy.ts
+++ b/packages/vite/src/node/server/middlewares/proxy.ts
@@ -55,7 +55,7 @@ export function proxyMiddleware(
             error: err
           }
         )
-        if (!res.writableEnded) {
+        if (!res.headersSent && !res.writableEnded) {
           res
             .writeHead(500, {
               'Content-Type': 'text/plain'