An inmate who hit a warden with a mop at Polmont Young Offenders' Institution has had 16 months added to his sentence.
Jed Duncan, from Aberdeen, was cleaning a corridor at the Stirlingshire facility when staff became concerned he was performing the task too slowly.
Falkirk Sheriff Court heard that the 21-year-old attacked the warden after being asked to hurry up.
The officer was unhurt in the incident which took place on 8 April last year.
Prosecutor Ann Orr told the court: "A prison officer asked him to hurry up. He started arguing and was told to go back to his cell.
"Reinforcements were called and he picked up a mop and struck the officer with its wooden handle."
Duncan had been due for release in August after serving a sentence for a series of offences including repeated joyriding, threatening and abusive behaviour, and assaulting a prison officer.