Facebook has restored access to its website after a 40-minute outage on Monday, the second time in a week that the site has gone down.
Users saw an error message that read "Sorry, something went wrong. We're working on it and we'll get it fixed as soon as we can."
Company shares were down nearly 4% at $89.25 (£58.83) shortly after the site went down. It also crashed on Thursday.
The social networking site is used by nearly 1.5 billion people worldwide.