Uncovering and explaining how our digital world is changing — and changing us.

This story is part of a group of stories called

Here’s a troubling data point if you’re a Facebook investor: The company may have finally tapped out its most valuable market, the U.S. and Canada.

Facebook’s daily active user base in the U.S. and Canada fell for the first time ever in the fourth quarter, dropping to 184 million from 185 million in the previous quarter.

It’s a very small decline in a market that Facebook already dominates. But it’s also Facebook’s most valuable market, and any decline in usership — even a small one — isn’t a great sign.

Each user accounted for $26.76 worth of revenue for the company last quarter, and it went up by 35 percent over the same quarter last year.

It’s not clear why that segment got smaller. But it has been a tough year for Facebook in the U.S., and most of the company has been grappling with the fact that Facebook’s service was used by Russian actors to try and sway the 2016 presidential election. Perhaps U.S users are grappling with that, too.

Overall, Facebook’s daily active user audience was up 32 million people in Q4. But it was the smallest quarter-over-quarter increase in two years.

Sign up for the newsletter Recode Daily Email (required) By signing up, you agree to our Privacy Notice and European users agree to the data transfer policy. Subscribe