Former Microsoft CEO Steve Ballmer said Friday he can see why investors could be worried the stock market is in a bubble.

“Are we in a market bubble or not? I don’t know. I’m silent on it. Where multiples are, etc., you could be a little worried,” Ballmer said on CNBC’s “Squawk Box.”

“I killed myself in the late ’90s when I said the stock market was overdone and we got a hiccup down the next day,” he said.

Since the election, as of Thursday’s close, the Dow Jones industrial average has surged more than 17 percent, the S&P 500 has gained 14 percent and the Nasdaq composite has risen 20 percent.

When asked whether President Donald Trump‘s pro-business policies have contributed to the market’s gains, he said: “I have no idea.”