The South African Constitutional Court has found that former president Jacob Zuma’s medical parole was improperly granted.
Zuma had been granted parole by Arthur Fraser, a former prison service chief who is thought to be a close ally of the former president.
After spending less than eight weeks of a 15-month prison term, he was freed in September 2021.
After refusing to cooperate with an anti-corruption investigation throughout his tenure in government, Zuma was found guilty of contempt.
He was recently observed in Zimbabwe at a climate conference.
The prisons department has said it is studying the constitutional court’s judgement and will comment after seeking legal advice.
This week marks the second anniversary of the deadly riots sparked by Zuma’s arrest. More than 350 people were killed in the violence.