The criminal court in French Polynesia has added two months to the jail sentence of a man imprisoned for killing a German tourist in 2011.
Arihano Haiti was found guilty of assaulting a fellow inmate three years ago when they were jailed in France.
The assault was caught on camera.
His defence lawyer said Haiti hit out after the fellow inmate threatened to rape his wife, according to Radio1.
Haiti is serving a 28-year sentence for shooting and then burning the tourist Stefan Ramin on Nuku Hiva.
He was also found guilty of sexually assaulting the German man's partner.
Haiti will have to serve at least 18 years before being eligible for parole.