Oscar Pistorius was sentenced to five years in prison in October, but the length of his jail sentence is not set in stone. The prosecution has won their bid for an appeal, meaning the former Olympian could have his stay in jail extended.

Two months after she found Pistorius guilty of culpable homicide for killing girlfriend Reeva Steenkamp, Judge Thokozile Masipa has decided that the prosecution can appeal the ruling. Now, the Supreme Court of Appeal must decide if Pistorius should have been found guilty of murder.

The double-amputee has admitted that he shot and killed his girlfriend on Valentine's Day 2013, but claims he thought it was an intruder who was standing behind his bathroom door. Prosecutor Gerrie Nel has contended that Pistorius deserves a stiffer sentence, even if he didn’t know he was firing his gun at Steenkamp, because he had an intent to kill whomever was in the bathroom.

The case will be reviewed by a panel of up to five judges, who can overturn Masipa’s decision. In order for the Supreme Court of Appeal to do so, the state must make a convincing argument that Masipa misinterpreted the law. Being convicted of murder would give Pistorius a jail sentence of at least 15 years.

Even if Pistorius’s sentence is not changed, the amount of time he spends in prison could be affected. The 28-year-old can be eligible for house arrest after 10 months, but it’s no longer likely that Pistorius will be out of prison by August.

Pistorius has reportedly been adjusting to life behind bars, where he is forced to spend 17 hours a day by himself in a cell. When he learned about the appeal, Pistorius did not take the news well, according to a report.

“He got up and stomped,” a source told South Africa Times. “He went straight to the gym. He started lifting weights like it was going out of fashion. He is p***** off.”