An extra second was added to the clock at midday on Sunday.
The decision was made by the International Earth Rotation Service at the Paris Observatory, which collects data to determine the exact length of a day.
The Measurement Standards Laboratory of New Zealand says our days are getting longer, because the earth's rotation is gradually slowing.
Without leap seconds, it says our clocks would get out of step with the time of day indicated by the position of the sun.
This new leap second was the 35th added since 1972.