A Thai military court has sentenced a 67-year-old man to 18 months in prison for writing insults against the country's monarch on the wall of a shopping mall restroom.

Human rights lawyer Sasinan Thamnithinan said Friday that the court found Opas Charnsooksai guilty of lese majeste — the crime of defaming, insulting or threatening the monarchy.

After taking over power from a civilian government in last May's coup, the junta has cracked down on criticism against the monarchy. It also has ordered lese majeste cases to be handled by military courts.

Sasinan says the court cut the original 3-year prison sentence in half because Opas confessed.

Opas has been detained since he was arrested last October.