Google has announced yet another update regarding the HTTPS ranking signal. They will flag invalid SSL certificates, which would prevent any boost from Google's HTTPS ranking factor.    
Google first announced HTTPS as a ranking signal in 2014. Then, Google announced they would begin indexing HTTPS URLs over HTTPS by default last month.

Today, John Mueller from Google tweeted that "Self-signed usually won't work in browsers, so we'd flag that."

Basically John is saying that if you receive an SSL certificate error from your browser, then Google will also detect that error. Because self-signed certificates often result in a certificate error, they should be avoided to ensure your HTTPS implementation is giving a boost to your site rankings.

What is a Self-Signed SSL Certificate?

A self-signed SSL certificate is not issued and verified by a trusted Certificate Authority (CA). They are signed by the same entity whose identity it certifies. Sites will generally go this route because the physical certificate is "free". In reality, the self-signed SSL certificate will cost them rankings, traffic, conversions and revenue.

To be safe, be sure to purchase the SSL certificate from a reputable third-party.

Aside from avoiding self-signed SSL certificates, you also need make sure there are not any other SSL certificate error on your site for both SEO and usability. There are several ways to check for errors:

1. Check for Browser Errors in Chrome

In Chrome, input the URL of the page you want to check and to the left of the URL in address you bar you should see 1 of 4 icons.

The following icons are indicators for site identity information:

The following icons are indicators for connection information:

2. Run a Test on SSL Labs

Enter your domain name to test the configuration of your SSL certificate for free on ssllabs.com. Once you input your domain name, the service conducts a deep analysis to find any errors. They also give a grade and provide help on how to improve the grade.

3. Check Google's Search Console for SSL Certificate Messages

Google has been known to send messages about SSL certificate errors to your Search Console Message Center. Be sure to frequently monitor your messages. You can also configure email notifications in your settings.

We know security is a top priority for Google, so be sure to check back for updates on Google's HTTPS ranking signal. If you have any questions or need help configuring your certificate, please let us know in the comments below.