Investors may want to take cover soon.
Art Cashin, UBS' director of floor operations at the New York Stock Exchange, says a "split personality" is manifesting itself in the stock market, and it could hit Wall Street where it hurts at any moment.
"We've been setting record new highs, and often the breadth has been negative. We've had more declines than advances," Cashin said Thursday on CNBC's "Futures Now."
"We're starting to get more new lows than new highs; 30 percent of the stocks in the S&P  are down for the year. Those are very unusual combinations with new record highs."
The divergences aren't the only factor creating concerns for Cashin, who's been a fixture at the New York Stock Exchange since 1964.
"I'm troubled by the market internals, and I'm very cautious about what is going in Washington," he added.
He's citing risks surrounding the viability of the GOP tax reform being debated in Congress. If lawmakers can't pull off passing a lower corporate tax rate, Cashin warned, stocks could "roll over" — and not in a good way.
"It's not expected, but it would be very negative," he said.
Even though he thinks a sell-off may be coming, Cashin isn't sure how deep it will be.
"We haven't had a drop of 3 to 5 percent in an abnormally long period. So, that would be my first target," said Cashin, who points out he's never seen an environment quite like this one. "You want to play it cautiously."