Here is a very small but telling sign of Elizabeth Warren’s growing momentum in the Democratic primary: Investors are now taking her seriously enough that her policy plans can affect stock prices.

On Friday morning—at 9:17 a.m., before markets opened, to be precise—Warren tweeted out her newest proposal, which would ban the use of private prisons in the United States. As she put it in a Medium post:

There should be no place in America for profiting off putting more people behind bars or in detention. That’s why I will shut down the use of federal private detention facilities by ending all contracts that the Bureau of Prisons, ICE, and the U.S. Marshals Service have with private detention providers. And I will extend these bans to states and localities by conditioning their receipt of federal public safety funding on their use of public facilities.

One key thing to note about this plan is that Warren wouldn’t need Congress to execute all of it—after all, federal contracts are handled by the executive branch. If you’re trying to price in the possibility of a Warren presidency (or a Democrat who is likely to follow Warren’s policy lead), this is the sort of proposal you really need to pay attention to.

And it appears Wall Street was, in fact, reading. As Bloomberg notes, stocks for private prison companies such as CoreCivic and Geo Group Inc. tumbled Friday.

Here’s the little cliff for the Geo Group, which as of publication was down more than 7.5 percent.

And here’s CoreCivic. Watch out below!

The political world has really started taking Warren’s candidacy seriously. The fact that stock prices are now falling based on her rhetoric just shows that the Wall Street types she rails against are taking her seriously too.