Bill Gurley, a venture capitalist who has invested in Uber and Snapchat, has issued a warning to unicorn investors.

In a lengthy essay posted on his personal blog, Gurley wrote that “there has been a fundamental sea-change in the investment community that has made the incremental unicorn investment a substantially more dangerous and complicated practice.”

The investor, who works for Benchmark Capital in Silicon Valley, said the unicorn phenomenon has put backers’ fortunes at risk.

“The pressures of lofty paper valuations, massive burn rates (and the subsequent need for more cash), and unprecedented low levels of IPOs and M&A, have created a complex and unique circumstance which many unicorn CEOs and investors are ill-prepared to navigate,” wrote Gurley.

The late-stage financing market had changed by the first quarter of 2016, according to Gurley. “Investors were becoming nervous and were no longer willing to underwrite new unicorn-level financings at the drop of a hat. Moreover, once high-flying startups began to struggle on the fundraising trail.”

Gurley claims that “anxiety has slowly crept back into everyone’s world.”

He adds: “As we move forward, it is important for all players in the ecosystem to realise that the game has changed.”

Gurley’s essay goes on to give advice to all of the people who are involved in the unicorn ecosystem including founders, CEOs, LPs, and employees.

There’s already an increase in startup failure, according to Gurley. “In addition to high profile companies like Fab.com, Quirky, Homejoy, and Secret, numerous other VC-backed companies began to shut their doors. There were in fact so many that CB Insights started a list. Layoffs have also become more prevalent. Mixpanel, Jawbone, Twitter, HotelTonight and many others made the tough decision to reduce headcount in an attempt to lower expenses (and presumably burn rate).”

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