Serverless: invalidArgumentError: invalid upgrade header. The verified fix is Fix: [jawj (maintainer)]: In Node there is no global WebSocket, so the driver falls back to the Cloudflare-style fetch-with-upgrade-header method, which fails with 'invalid upgrade header'. Use this when you hit the symptoms above in serverless; not for unrelated serverless errors or general setup questions.
TL;DR
Fix: [jawj (maintainer)]: In Node there is no global WebSocket, so the driver falls back to the Cloudflare-style fetch-with-upgrade-header method, which fails with 'invalid upgrade header'.
The error
Is the connection string the right URL? `invalid upgrade header` sounds like a websocket error, so I'm wondering if I was supposed to use the connection string or maybe a URL for the proxy.
Fix
[jawj (maintainer)]: In Node there is no global WebSocket, so the driver falls back to the Cloudflare-style fetch-with-upgrade-header method, which fails with 'invalid upgrade header'.
Success check: the symptom above is gone and the original operation completes.
When to use
You hit this exact symptom in serverless.
You want the verified fix without digging through the thread.
When not to use
A different error in serverless, even a similar-looking one.
General serverless setup or credential questions.
Compatibility
Serverless (neondatabase/serverless)
Variant phrasings
How to fix "invalidArgumentError: invalid upgrade header" in serverless
Published guidance. View the version history for earlier changes.
Published recentlyPublished Oct 3, 2026. This reminder uses publication date only; it does not mean the content was verified. Review again after Apr 1, 2027.
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Published recentlyPublished Oct 3, 2026. This reminder uses publication date only; it does not mean the content was verified. Review again after Apr 1, 2027.