The International Earth Rotation and Reference Systems (IERS) announced an extra second will be added at the end of June to account for a discrepancy between Earth’s rotation and the atomic clock.

The extra second will be added as the clock strikes midnight universal time, meaning the extra second will come for people in the United States at 8 p.m. EDT.

Leap seconds can be added in June or December, according to IERS. There have been 25 instances since 1972 of an extra second being added.

When the time comes, clocks synchronized to standard civil time will show the extra second as :60, however it’s possible that programs not equipped to handle the extra second could have an issue.