A wave of speculative buying has crashed over the stock market to start the new year, prompting CNBC’s Jim Cramer to urge investors to take profits in stocks that have gone parabolic.

“You haven’t made a profit unless you ring the register on some of your gains,” Cramer said Tuesday night on “Mad Money.” Those are simply “paper gains. That doesn’t count,” he said.

“Let’s say you have a big gain in a stock that’s soared this year, tomorrow [you should] take something off the table,” Cramer said.

Cramer identified more than 30 U.S.-listed stocks with a market capitalization above $1 billion that had gained at least 50% year to date as of Friday’s close. Stocks that check all those boxes are where investors should look to trim, he said.

“For the most part, they’re companies with no earnings and little in the way of sales,” Cramer said, explaining that the trading in this cohort echoes the speculation seen late last summer in areas like quantum computing, cryptocurrencies and alternative energy.

In late September, Cramer started to sound the alarm on what he deemed excessive market froth and implored investors do some selling in red-hot names with little earnings to justify their valuations. Eventually, many high-flying stocks such as nuclear play Oklo got hit hard during the fall and remain well off their highs.

“Back then, I excoriated those who failed to take profits. I was loud and noisy about it and I’m doing the same right now tonight,” Cramer said. He continued, “I’m not advocating that you sell everything, I’m advocating that you try to take a big percentage of your stock and put it in cash. That way you’re playing with what I call the house’s money.”    

Cramer’s comments Tuesday came on the heels of a broader market pullback as President Donald Trump ratcheted up his rhetoric on Greenland with tariff threats.