A leap second will be inserted in the world's clocks just before midnight, Greenwich mean time, on New Year's Eve, the U.S. Naval Observatory reported Friday.
That means 7 p.m. EST, Dec. 31, will occur one second later than it would have otherwise.
Leap seconds are needed occasionally because modern atomic clocks measure time with great accuracy, while the rotation of the Earth can be inconsistent.
The rotation of the Earth has been slowing down, so leap seconds keep the clocks and the Earth from getting out of synch with one another.
This will be the 23rd leap second that has been inserted since 1972 when an international timekeeping agreement was signed, according to the Observatory. The last one was inserted seven years ago.