An NYPD report says nearly one in six undercover officers has been mistaken for a suspect by fellow officers — and come face to face with a loaded gun.

The report comes after an off-duty officer in plainclothes was killed by another cop on May 28. The off-duty officer had drawn his gun and was chasing a man who had broken into his car when the other officer mistook him for an armed suspect and shot him.

Such cases are rare.