Indonesian supreme court has ruled that school teachers acquitted in a case of sexual abuse will have to serve a year more in prison in addition to the original sentence.

Under the apex court's verdict, Canadian national Neil Bantleman and Indonesian teaching assistant Ferdinand Tjiong will have to serve a new 11-year sentence after they were found guilty of sexually abusing three young children at an international school.

The two teachers had been convicted of sexually abusing students at Jakarta International School and they were awarded a 10-year sentence. However, they were acquitted in August 2015.

The supreme court overturned the acquittal and added another year to their original sentence.

"They have been sentenced again to 11 years," Supreme Court spokesman Suhadi told Reuters.

The men were arrested in July 2014 after parents of a 6-year-old boy at the school alleged that he'd been sodomized, according to the Jakarta Post.

The trial court had sentenced four male janitors to eight years in prison and a woman to seven years in prison. A sixth suspect had killed himself in custody.