A South African court has ruled that the decision to drop corruption charges against President Jacob Zuma can be reviewed.
The charges were dropped just weeks before the 2009 election which led to Mr Zuma becoming president.
The court agreed with a request from the opposition Democratic Alliance (DA) to challenge the decision.
The judges said judicial reviews were the "best guarantee against tyranny, now and in the future".
Mr Zuma is facing increased criticism from some members of the governing African National Congress (ANC) ahead of its decision in December on whether to retain him as its leader for the next election, scheduled for 2014.
The ANC candidate would be the strong favourite to become president.
The corruption charges relate to a controversial $5bn (£3.4bn) 1999 arms deal, which led to Mr Zuma's financial advisor, Schabir Shaik, being convicted of soliciting a bribe in 2005.
After Shaik's conviction, Mr Zuma was sacked as deputy president before being charged himself.
Mr Zuma has always denied any wrongdoing and last year announced a government inquiry into the deal.
Backing the DA's request for a judicial review into the National Prosecuting Authority decision to drop the charges against Mr Zuma, the judges of the Supreme Court of Appeal wrote that the concept "means that none of us is above the law".
"It is a concept that we, as a nation, must cherish, nurture and protect. We must be intent on ensuring that it is ingrained in the national psyche. It is our best guarantee against tyranny, now and in the future."
The DA also wants the prosecutors to reveal why the charges were dropped.
At the time, chief prosecutor Mokotedi Mpshe said that phone-tap evidence suggested the investigation had been manipulated for political reasons.
"It was pure abuse of process," Mr Mpshe said.
Mr Zuma's supporters always maintained that his prosecution was part of a campaign by allies of his bitter rival, former President Thabo Mbeki.
Mr Zuma finally replaced Mr Mbeki as ANC leader in December 2007.