Humanity should be wary of seeking out contact with alien civilizations, Stephen Hawking has warned once again.

In 2010, the famed astrophysicist said that intelligent aliens may be rapacious marauders, roaming the cosmos in search of resources to plunder and planets to conquer and colonize. He reiterates that basic concern in “Stephen Hawking’s Favorite Places,” a new documentary streaming now on the CuriosityStream video service.

“One day, we might receive a signal from a planet like this,” Hawking says in the documentary, referring to a potentially habitable alien world known as Gliese 832c. “But we should be wary of answering back. Meeting an advanced civilization could be like Native Americans encountering Columbus. That didn’t turn out so well.”

For what it’s worth, some other astronomers believe Hawking’s caution is unwarranted. Any alien civilization advanced enough to come to Earth would surely already know of humans’ existence via the radio and TV signals that humanity has been sending out into space since 1900 or so, this line of thinking goes.