Next time you don't recognise someone claiming to be an old friend, just tell them you've hit your face limit.
Scientists in the UK have found humans can remember 5000 faces on average.
"The ability to distinguish different individuals is clearly important - it allows you to keep track of people's behaviour over time, and to modify your own behaviour accordingly," said Rob Jenkins of the University of York, who co-authored the study.
The range was wide, though - some could remember 10,000, while others topped out at 1000.
"The range could be explained by some people having a natural aptitude for remembering faces. There are differences in how much attention people pay to faces, and how efficiently they process the information," said Dr Jenkins.
"Alternatively, it could reflect different social environments - some participants may have grown up in more densely populated places with more social input."
What the study didn't uncover was whether we accumulate recognisable faces as we age, or forget old ones to make way for the new. It also didn't measure whether we could remember the 5000 names that go with the faces.
The study, published in journal Proceedings of the Royal Society B: Biological Sciences, is believed to be the first scientific estimate of how many faces we can remember.
"Given the social lives of our ancestors, the ability to recognise thousands of individuals might seem like overkill," Dr Jenkins told The Guardian.
"But there are plenty of examples of overkill in nature. The venom of some spiders can kill a horse, even though the spider presumably has no ambitions to eat the horse."
The research may help develop better facial recognition artificial intelligence.