If you’re having issues with someone on Facebook, you can always block them.

It’s a last resort, but sometimes it’s inevitable when a friend gets on your nerves. However, if you’re upset with Facebook founder Mark Zuckerberg, don’t expect that “block” button to do much of anything. Click on it, and you’ll be greeted with the following message:

Don’t bother trying again; Zuckerberg is unblockable, according to a recent report from BuzzFeed News.

This actually isn’t a new issue. TechCrunch reported on Zuckerberg’s iron-clad profile way back in 2010. At the time, the error message was different, but the problem remained essentially the same: For Facebook users, Zuckerberg is off limits—for the time being, anyway.

Facebook insists that the problem isn’t specific to Zuckerberg’s profile.

In fact, many high-profile accounts can’t be blocked, according to a Facebook spokesperson quoted by The Telegraph. The good news? There’s actually a reason for this strange “feature.”

“It’s generated when a person has been blocked a certain large number of times,” the spokesperson said. “In very rare instances, a viral campaign will develop instructing lots of people to all wrongly block the same person.”

In other words, too many people have blocked Zuckerberg already, so Facebook’s algorithm has determined that there’s an active campaign to discredit the philanthropist. As a result, the site has put a freeze on his profile’s block button.

As crazy as that might sound, there’s some precedent, according to Facebook’s development team.

The site has more than 2 billion monthly active users, and each year, thousands of campaigns try to capitalize on those users by taking advantage of the social network’s sharing algorithms.

For example, Facebook recently revealed that fake Russian accounts purchased more than $100,000 in political ads from June 2015 to May 2017. A post from Facebook’s chief security officer, Alex Stamos, accused a Russian company called the Internet Research Agency of purchasing the ads.

“We don’t allow inauthentic accounts on Facebook, and as a result, we have since shut down the accounts and Pages we identified that were still active,” Stamos wrote.

We know we have to stay vigilant to keep ahead of people who try to misuse our platform. We believe in protecting the integrity of civic discourse, and require advertisers on our platform to follow both our policies and all applicable laws. We also care deeply about the authenticity of the connections people make on our platform.

Facebook also recently announced technology improvements intended to identify and eliminate these types of malicious campaigns and block users who try to create fraudulent accounts. While the company is tight-lipped about the exact processes it uses to identify potential problems, the Zuckerberg blocking issue shows that Facebook looks at a wide range of factors in making its decisions.

For the time being, Zuckerberg is still unblockable, but the site’s spokesperson told BuzzFeed News that a fix will eventually roll out. Until then, Facebook users can still unfollow Zuckerberg.