Several Russian Internet providers briefly blocked access to Google.ru on Thursday, after the domain appeared on the “out-load” list operated by Roskomnadzor, Russia’s federal censor, Meduza reports.

By 4:15 p.m. on Thursday, Google.ru had disappeared from Roskomnadzor’s out-load list. In the roughly three hours that the search engine’s Russian domain spent on the blocklist, several major Internet providers, including Akada and TTK, began cutting off access to the website.

Roskomnadzor officials later explained that Google accidentally landed on the blocklist because Russia’s Federal Tax Service provided the censor with a link to an advertisement to an online bettering service. It remains unclear why the tax service sent Roskomnadzor a link to the betting website’s Google advertisement instead of a direct link to the site.

The out-load list is a special database of prohibited websites. Russian Internet providers are supposed to download this database twice a day, at 9 a.m. and at 9 p.m. They then have to block the “out-load” webpages, so that customers can’t access these websites. If someone tries to access a blocked website, they see a page showing a notification that the website was blocked. It usually says, “We are sorry for the inconvenience, but access to the requested page has been limited by the state authorities.”