Elon Musk is one of the most influential people on Twitter for a reason.

So when Musk shared Monday night that Tesla currently has “no contract” signed with Hertz, Tesla’s stock fell as much as 4%, which sets the company up to lose $42 billion in market value, according to Forbes

The single tweet—which comes after Tesla shares have blown up 33% since Hertz announced it was buying 100,000 of its vehicles by the end of 2022—puts Tesla’s largest order to date in question. Musk also shared that the “Hertz deal has zero effect on our economics.”

“If any of this is based on Hertz, I’d like to emphasize that no contract has been signed yet,” Musk replied to a Twitter user who showed the Tesla stock growing at an impressive rate. “Tesla has far more demand than production, therefore we will only sell cars to Hertz for the same margin as to consumers,” he added.