About 20% of Uber riders tip their drivers, according to a new CBS interview with CEO Dara Khosrowshahi. For Khosrowshahi, that amount seems to be just fine.

“You should only tip if you feel you got your money’s worth and then some,” the CEO told CBS News Sunday Morning. In the US, Khosrowshahi said, there’s a pressure and expectation to tip.

That’s probably not music to the more than 7 million Uber drivers’ ears: tips aren’t required on the app but they certainly help to pad drivers’ wages. Recent research by New York’s Columbia Business School found that Uber’s shifting algorithms had cut driver pay on billions of trips.

There’s also the matter of Khosrowshahi telling The Wall Street Journal earlier this year that human driver displacement from autonomous vehicles will occur within the next 15 to 20 years.