His stupid mistake will land him in jail for a year.

Occupy Wall Street protester John Scott Dekuyper, who was busted for packing a gun when he showed up at court to face charges of trying to swipe a cop’s badge, pleaded guilty to the weapon charge yesterday.

Dekuyper, 53, is guaranteed a year in jail.

He dubbed his gun gaffe “the stupidest thing I’ve ever done.”

A court officer caught Dekuyper with an unloaded Colt .45 and bullets in February 2012.

The previous October, he allegedly made a grab for NYPD Chief Joseph Esposito’s shield.

He’ll return for his sentencing in September.