A South African court has rejected an appeal by the former financial adviser to ex-Deputy President Jacob Zuma, Schabir Shaik.
Shaik's trial raised questions about Zuma's conduct
Shaik was last year sentenced to 15 years in prison for fraud. He now has 45 hours until he must start his term.
At the time judge Hilary Squires said Shaik's relationship with Mr Zuma, who is seen as a possible future president, was "generally corrupt".
Correspondents say the verdict will be a blow to Mr Zuma.
Shaik's conviction and the judge's comments prompted President Thabo Mbeki to sack Mr Zuma.
He, too, was then charged with corruption but the case was thrown out in September.
Mr Zuma's chances of becoming South Africa's president in 2009 elections, could whether prosecuters still investigating Mr Zuma for corruption decide to bring fresh charges.
Following the appeal decision, they said the Shaik appeal had been one of the things holding them back.
'Wealth of evidence'
Shaik was found guilty for receiving money from the French arms company, Thomson-CSF, to facilitate a deal worth more than $4bn.
"We find that a wealth of evidence to show that the friendship [between Shaik and Zuma], which we accept exists, was persistently and aggressively exploited by Mr Shaik for his own and his group's advantage," appeal court Judge Craig Howie said at the ruling on Monday morning.
"The only reasonable inference is that the payments were corruptly made to influence Mr Zuma to act in conflict with his constitutional duties and thereby enhance Mr Shaik and his group's business interests."
Jacob Zuma is seen as more charismatic than President Mbeki
He said that the Supreme Court of Appeal found no reason to reduce Shaik's jail sentence for two counts of corruption and one of fraud.
Mr Zuma and Shaik were both charged over the 1999 arms deal.
The corruption case against Mr Zuma was thrown out two months ago because the prosecution said they were still not ready to start the trial more than a year after he was charged.
The prosecution, however, say they may still press new corruption charges against the former deputy president.
Unless this happens, Mr Zuma would be free to contest next year's leadership contest of the ruling African National Congress (ANC).
Mr Zuma was also acquitted on separate rape charges earlier this year - his supporters say there is a political vendetta against him, designed to remove him from the race to succeed Mr Mbeki in 2009.
Whoever is elected to head the ANC would be favourite to become South Africa's next president.