LINCOLN, Neb. (AP) — A Nebraska inmate already serving 35-40 years could be sentenced to 20 more years because he assaulted a prison guard.

Online court records say 25-year-old Brendan Horner pleaded no contest Thursday after prosecutors lowered the charge in exchange for Horner’s plea. His sentencing is scheduled for June 15.

Horner grabbed the guard March 26 last year at the Nebraska State Penitentiary when the guard entered the cell to look for marijuana the guard smelled. Prosecutors say Horner threw the guard to the floor and punched the guard several times before other guards intervened.

Horner’s been serving time for shooting a man during a June 2012 road rage incident in Lincoln.