Mark Cuban is coming around on high-frequency trading firms.

Cuban, who warned four years ago that the industry was creating structural and trading risks for the market, said Tuesday he bought shares of high-frequency trader Virtu Financial Inc.

That’s a turnaround from March 31, 2014, the day Michael Lewis’s book “Flash Boys” came out, in which he blasted high-speed traders. “There’s no such thing as bug-free software,” Cuban said that day in an interview on CNBC, calling it the greatest risk to that type of trading. “When you have fat-finger bugs you just don’t know what’s going to happen to the market.”

The billionaire explained Tuesday on CNBC that he invested in Virtu because “they make money off of volatility.” Shares of Virtu have rallied over the past week as volume and volatility increased in financial markets.