Elon Musk is concerned about the future of humanity. The tech entrepreneur shared a link with his 21 million Twitter followers Friday morning, urging them to watch Chris Paine’s latest movie Do You Trust This Computer?. Musk wrote that “nothing will affect the future of humanity more than digital super-intelligence,” while paying homage to the late Stephen Hawking that shared the same concerns.

Paine’s movie, available for free streaming until Sunday night, looks at how machine intelligence has become a pervasive part of everyday lives. It also explores how users trust smartphones and social networking with their data, an issue that’s seen newfound attention in recent weeks as it emerged that Cambridge Analytica may have harvested 87 million Facebook users’ data. Paine shared a trailer for the movie on its Facebook page — unlike Musk, it seems Paine has yet to fully sign up to the #DeleteFacebook movement spurred by the Cambridge Analytica scandal:

It’s an issue that Musk highlighted regularly, fearing that A.I. could overtake humans if not properly managed. He’s not against A.I. in general, with Tesla using machine learning to develop an autonomous driving system, but in November 2017 he evoked Nate Dogg and Warren G in a call to “regulate.”

Musk has recommended Paine’s work before, praising his 2006 documentary Who Killed the Electric Car as an outline of the failure of General Motors’ EV strategy. Paine’s 2011 followup Revenge of the Electric Car documented Musk’s early years at Tesla that aided the rebirth of the market, leading to the Nissan Leaf and Tesla Roadster.

Neuralink, a secretive startup outlined by Musk in April 2017, could hold the answer to the issued raised by the documentary. It proposes a brain-computer interface to develop a symbiotic relationship between human and machine. A report last week suggested Neuralink planned to turn its San Francisco headquarters into an animal testing facility.

The alternative? Hawking warned in November 2017 of an A.I. developing into “a new form of life that outperforms humans.”