The law, passed in early April, makes the deliberate spread of false information punishable by up to six years in jail and a hefty fine.
It has sparked outrage from rights groups, who believe the law could be used to crack down on dissent, especially criticism of then-prime minister Najib Razak ahead of the May 9 vote.
Najib’s ruling Barisan Nasional coalition, which ruled Malaysia uninterrupted for 61 years since independence, was routed at the polls by a Mahathir-led opposition alliance.
Mahathir, who ruled Malaysia for 22 years as prime minister before stepping down in 2003 and came back from retirement to take on Najib, said the law would be reviewed to give a clearer definition of fake news.
“The fake news law will be given a definition that is clear,” he said in a special address on national television.
“People and news companies will understand what is fake news and what is not fake.”
Mahathir himself was criticised for clamping down on the media during his earlier term as premier. But he said in his speech Sunday his government would not restrict the press even if they came up with news the government found uncomfortable.
But the 92-year-old — the world’s oldest elected leader — added that “action” would be taken if false news was disseminated with the intention to cause chaos.
“Even though we support the concept of freedom of the press and freedom of speech, everything has a limit,” he said.
The law has so far been used to convict one person: a Danish man who was jailed for a week for accusing emergency services of responding slowly after a Palestinian Hamas member was gunned down in Kuala Lumpur in April.
Mahathir himself was probed during the election campaign for allegedly spreading fake news after claiming that a plane he was supposed to take may have been sabotaged.
Malaysia ranks 145th out of 180 countries in the 2018 World Press Freedom Index, with number one being the freest.