ERR_QUIC_PROTOCOL_ERROR
Chrome tried the newer QUIC protocol (HTTP/3, over UDP) and the connection broke. Something between you and the site is interfering with it.
Quick checks
- Reload; Chrome usually falls back to TCP on the next try.
- Try another network.
- Disconnect VPNs and pause security software.
Fixes on Mac
Disable QUIC to confirm
- Open
chrome://flags/#enable-quic, set it to Disabled, relaunch. - If the error disappears, the network breaks QUIC. Leave it disabled on that network, or report it to whoever runs it.
- Open
Check filtering software
- Content filters and firewalls that inspect traffic sometimes block or corrupt UDP 443.
Fixes on Windows
Disable QUIC and check antivirus
- Same Chrome flag; also test with antivirus web protection paused.
Other devices
Router
- Update router firmware; some routers mishandle UDP fragments.
Still not working?
Site owners: if users report this only for your site, check your CDN or load balancer's HTTP/3 settings and UDP 443 firewall rules. Browsers advertise HTTP/3 via the Alt-Svc header; removing it disables HTTP/3 for clients.
See what’s happening
LightAtom's connections view shows Chrome's UDP traffic (QUIC) grouped per app, so you can see whether it's used.
Frequently asked questions
What is QUIC?
A transport protocol over UDP that HTTP/3 uses. It sets up connections faster than TCP plus TLS and handles packet loss better, but some networks block or break UDP.
Is it safe to disable QUIC in Chrome?
Yes. Chrome then uses HTTP/2 over TCP, which is just as secure and only slightly slower in some conditions.
Why does QUIC fail on my network?
Firewalls that only allow TCP web traffic, deep-inspection devices, or VPNs that mishandle UDP. Corporate networks often block it on purpose.