Unless you’re the world’s richest person, you shouldn’t be buying Bitcoin. That’s the message from Bill Gates – the third richest.

With a rally of more than 400% over the past year, Bitcoin has become increasingly mainstream, and everybody including prominent investors and policy makers have been talking about it. The world’s on-again, off-again richest person, Elon Musk, recently invested $1.5 billion in the cryptocurrency through his company, Tesla Inc., and said Bitcoin would soon be accepted for payments.

For Gates, it’s not something Main Street should buy into – plus it’s bad for the environment as mining the coins requires a lot of energy.

“Elon has tons of money and he’s very sophisticated, so I don’t worry that his Bitcoin will sort of randomly go up or down,” Gates said in an interview with Bloomberg Television’s Emily Chang. “I do think people get bought into these manias who may not have as much money to spare. My general thought would be that if you have less money than Elon, you should probably watch out.”

Musk himself has repeatedly boosted Bitcoin on Twitter and other platforms.

Musk, who’s worth $189.6 billion as per the Bloomberg Billionaires Index, has been an avid supporter of Bitcoin — so much so that he’s influenced the token’s price. It surged as much as 76% this month following Tesla’s investment, before tumbling 13% after he tweeted the prices of cryptocurrencies “do seem high.”

Bitcoin was trading around $51,400 at 8:30 a.m. in New York on Thursday.

The debate over Bitcoin isn’t new. Billionaire Warren Buffett deems cryptocurrencies have no value and don’t produce anything. Treasury Secretary Janet Yellen, another long-time skeptic, said at a New York Times conference earlier this week that Bitcoin is an “extremely inefficient way of conducting transactions.”

But with more and more companies starting to accept Bitcoin — as PayPal Holdings Inc., Visa Inc. and MasterCard Inc. recently have — the token has gained wider acceptance. As central banks including the Federal Reserve and European Central Bank are studying how to digitalize their own sovereign currencies, and firms such as Fidelity Investments Inc. launch funds letting investors add cryptocurrencies to their portfolios, the debate is here to stay.

(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)