Market will crash, just don't know catalyst: Marc Faber

Marc Faber: Global economy not supporting valuations
Marc Faber: Global economy not supporting valuations

The market is setting up for a big decline that could be as bad as the crash of 1987, according to Marc Faber, known as "Dr. Doom." He just isn't sure exactly what will set it off.

"The problem with crashes, you never know beforehand precisely what is the catalyst," the publisher of the Gloom, Boom & Doom report told CNBC's "Closing Bell."

It could come from the credit market, equities being perceived as too expensive or a geopolitical event, he added.

His comments came a day after he told "Futures Now" that the asset bubble has begun to burst.

Read MoreMarc Faber: The asset bubble has begun to burst

"I think it's a colossal bubble in all asset prices, and eventually it will burst, and maybe it has begun to burst already," Faber said Tuesday.

Marc Faber
Adam Jeffery | CNBC

He's calling for a 30 percent decline in the .

"I think that the global economy does not support the current valuations," he said Wednesday. Corporations "have had record profits, largely because they are buying back their own shares and so the number of shares is diminishing where revenue growth is basically flat."

Read MoreFaber and Schiff may be just what this rally needs

In fact, he said the bond market, which is more sophisticated than the stock market, does not believe in a strong economic recovery and neither does he.

Faber has been calling for a major correction for years. So far, the market hasn't followed his theory, but he said that could be setting it up for an even bigger fall.

"Since 2012, I said it would be healthy for the markets to have a meaningful correction, but it could be that we are in a year like '87 when we go straight up and then we don't have a correction but a more significant crash," he said.

Read MoreMarket that's up 22% holds its breath for Thursday

—By CNBC's Michelle Fox. CNBC's Alex Rosenberg contributed to this report.