The charity Medecins Sans Frontieres is tracking down thousands of people who donated to its tsunami fund, in order to redirect or refund their money.
MSF was given far more money than it needed for its tsunami operations
Response to the disaster was so good that the charity raised four times the amount it needed, despite closing its appeal only a week after the tsunami.
An MSF spokeswoman told the BBC that the situation was "extraordinary".
But she said that only 1% of donors contacted had refused to allow their money to be used for other projects.
Anouk Delafordrie, from MSF's headquarters in Geneva, said that the charity initially thought it would need 40m Euros ($52m) to fund its tsunami projects - a figure it later revised to 25m Euros ($32m).
But the unprecedented generosity of donors from around the world netted the charity a total of 105m Euros ($135m) - leaving it with far more cash that it had bargained for.
The charity then set about contacting donors by telephone and letter, to ask permission to redistribute the funds to other projects the charity was involved with.
"Less than 1% of people refused to let us use the money elsewhere," said Ms Delafordrie.
Flooded with donations
The Australian branch of MSF was one of those given far too much money for its tsunami-related projects.
According to James Nicholls, a spokesman for MSF Australia, the charity's tsunami appeal raised more than Aus$2.5m (US$1.9m) in the three days it was open. It only needed Aus$1m (US$0.8m).
"We closed our appeal very quickly, so fortunately we don't have a huge number of people to contact," Mr Nicholls said.
"I think people gave so much money because it was such a big disaster, and it was covered so extensively by the media," he added.
"People thought, 'It could happen to us,'" he said. "They can identify with it more than with other humanitarian disasters, like victims of conflict or civil war."
But Mr Nicholls was anxious to point out that MSF still needed funds.
"We do, absolutely, need money for other projects. Our biggest operation at the moment is in Darfur, Sudan, where one and a half million people are in desperate need," he said.