The flag to mark the 15th anniversary of Hong Kong's handover to the mainland will be raised a bit late - by one second.
That is because at 7:59:59 am on July 1, Hong Kong time, a leap second will be added, in accordance with the addition to co-ordinated universal time (UTC), the primary standard by which the world regulates clocks.
The police officer responsible for raising the flag - which is supposed to be at the top of the pole at 8am - will have to be sure his watch is in synchronisation with UTC, and not the mean solar time, which is based on the earth's rotation.
So the first day chief executive-elect Leung Chun-ying takes office will be a second longer.
A leap second is an extra second added every few years to keep time measured by atomic clocks in sync with the time based on the earth's rotation, which has been slowing.
The Hong Kong Observatory took care to announce the news last month - more than two months in advance this time because some companies had problems with their computer servers on previous occasions, according to the Observatory's scientific officer, Woo Wang-chun. It used to do so two weeks prior to when the extra seconds were added or subtracted.