Tesla and SpaceX CEO Elon Musk implored Trump supporters to vote at Saturday’s rally in Butler, Pennsylvania, saying, “This will be the last election” if they do not.

After Trump invited him on stage to speak, Musk declared that Trump must win the election to “preserve the Constitution” and “democracy” before calling on those at the rally and watching around the country to register to vote.

“This is a must-win situation. Must win. So I have one ask for everyone in the audience, everyone who watches this video, everyone on the live stream. It’s this one request. It’s very important: Register to vote,” Musk said, adding folks should ensure others they know are registered to vote as well.

“Text people now, now!” he said. “And then, make sure they actually do vote. If they don’t, this will be the last election. That’s my prediction. Nothing’s more important.”

Musk noted that everyone attending the rally is likely “already convinced” and made an appeal directly to those watching remotely, pointing to the rapidly approaching voter registration deadlines in crucial swing states:

You need to get everyone you know at work, your friends, family, text groups, your social media, everything, get them to register to vote right now, only two days left for Georgia and Arizona, only a couple weeks left in Pennsylvania, and if they’re not registered to vote, it doesn’t matter at that point.

He said that a margin of as little as 500 to 1,000 votes could decide the next president.

“A lot of people think maybe their vote doesn’t count. Well, it does,” Musk emphasized. “It matters. And this election could be decided by 1,000 votes, 500 votes, a tiny margin.”