Oscar Pistorius could be convicted of murder after a court ruled in favour of an appeal against his conviction for culpable homicide.
Prosecutors from the Paralympian's trial for killing girlfriend Reeva Steenkamp want him convicted of the more serious charge.
A court in Johannesburg saw Gerrie Nel successfully argue against defence lawyer Barry Roux, who claimed the appeal process should never have been allowed to begin.
Pistorius is serving five years but could face 25 years in jail if the appeal against his sentence succeeds.
Judge Thokozile Masipa, who also presided over the lengthy trial of the 28-year-old, said there was "nothing new" in the defence's argument against the appeal.
Pistorius is South Africa's most high-profile prisoner. There was controversy this week when video emerged of him playing football in a prison yard with a Czech criminal.
The appeal against Pistorius's sentence shall be heard at the Supreme Court of Appeal.