What does ERR_SSL_PROTOCOL_ERROR mean?

The browser could not set up a secure TLS connection because the server’s answer was invalid or unsupported. The browser stops, because it cannot make sure the connection is safe.

Is ERR_SSL_PROTOCOL_ERROR a certificate problem?

Not always. A certificate problem usually gives a warning such as “Your connection is not private”. This error means the secure handshake itself failed, which points to the TLS settings, the port or something on the path.

How do I fix ERR_SSL_PROTOCOL_ERROR on my website?

Check that port 443 really serves TLS, allow TLS 1.2 and TLS 1.3, and check that the certificate is installed for the host name. If you use a CDN, check its SSL mode.

Can a wrong clock cause ERR_SSL_PROTOCOL_ERROR?

A wrong date and time more often cause a certificate date error, but they can also break a secure handshake. Set the clock to automatic and try again.

ERR_SSL_PROTOCOL_ERROR

ERR_SSL_PROTOCOL_ERROR: what it means and how to fix it

ERR_SSL_PROTOCOL_ERROR means the browser started a secure (TLS) connection and the server’s answer was not valid. The server may not speak TLS on that port, the two sides may not share a TLS version, or something on the path changes the traffic.

You may also see

“This site can’t provide a secure connection” (Chrome)
SSL_ERROR_RX_RECORD_TOO_LONG (Firefox)
“Secure connection failed” (Firefox)

Common causes

1
The server answers plain HTTP on the port the browser uses for HTTPS.
2
The server only offers old TLS versions that current browsers no longer accept.
3
The server or a CDN is set up for the wrong host name, so the handshake gives a wrong answer.
4
The clock of the device is wrong, or a security program or proxy scans and changes the secure traffic.
5
An experimental browser feature, such as QUIC, fails on your network.

If you are visiting the site: how to fix it

1
Check that your date, time and time zone are correct, then reload.
2
Clear the browser cache and cookies, and try an incognito window and another browser.
3
Turn off a VPN, a proxy and the HTTPS scanning of your security program, to test.
4
In Chrome, if the error stays, turn off the experimental QUIC protocol in chrome://flags to test.

If you run the site: what to check

1
Check that port 443 serves TLS and not plain HTTP. A web server with a listen line that lacks ssl is a common cause.
2
Allow TLS 1.2 and TLS 1.3, and use a current list of ciphers.
3
Check that the certificate is installed for the host name, and that the virtual host answers for that name.
4
If a CDN sits in front, check its SSL mode and that the origin matches it.

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Frequently asked questions

What does ERR_SSL_PROTOCOL_ERROR mean?: The browser could not set up a secure TLS connection because the server’s answer was invalid or unsupported. The browser stops, because it cannot make sure the connection is safe.
Is ERR_SSL_PROTOCOL_ERROR a certificate problem?: Not always. A certificate problem usually gives a warning such as “Your connection is not private”. This error means the secure handshake itself failed, which points to the TLS settings, the port or something on the path.
How do I fix ERR_SSL_PROTOCOL_ERROR on my website?: Check that port 443 really serves TLS, allow TLS 1.2 and TLS 1.3, and check that the certificate is installed for the host name. If you use a CDN, check its SSL mode.
Can a wrong clock cause ERR_SSL_PROTOCOL_ERROR?: A wrong date and time more often cause a certificate date error, but they can also break a secure handshake. Set the clock to automatic and try again.

Know about it before your visitors do

Uptrack checks the certificate on a schedule and alerts you before it expires, so an expired certificate never becomes a warning page for your visitors.

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