In an interview with Fortune’s Dan Primack at the Upfront Summit in Los Angeles on Thursday, Wilson expressed his frustration at tech companies taking their time going public. As Fortune previously reported, 2015 was the slowest year since 2009 for tech company IPOs. Wilson compared the process to taking medicine. It’s unpleasant, but it’s good for you—and Kalanick is chickening out.

Uber currently has a valuation of over $62 billion and is continuing to raise capital in the private market. The CEO still thinks that the company needs to mature and is “nowhere near” an IPO.

“He’s wimping out,” Wilson told Primack. “That should be a publicly traded company.” He says that investors will want their money back at some point, and Kalanick has a responsibility to make sure that happens. “You can’t just say f— you. Take the goddamn company public.”