Basically, the court just guaranteed that millions of customers would stay on with insurers, and that’s made investors very happy. The ruling gave some much needed clarity to stockholders concerning the fate of companies that benefit from the higher number of insured brought about by the Affordable Care Act.

The biggest public insurers in the U.S., including UnitedHealth, Anthem, Aetna, Humana and Cigna, are all up in mid-morning trading. The biggest gains so far have gone to Humana, up 2.4%, and UnitedHealth, up 1.7%.

While the Supreme Court’s Obamacare move is beneficial to these companies, some of the gains could also be attributed to the high level of acquisition interest floating around the insurance industry these days.

The King v. Burwell decision has also been great news for hospitals — more insured customers means more secure payments. HCA Holdings, Tenet Healthcare and Community Health Systems all gained at least 9% after the ruling.

In the King decision, the Court voted 6-3 to uphold subsidies for Americans signing up for Obamacare in states that used the national insurance exchange instead of developing their own state-specific exchanges. The decision kills off what was one of the most potentially lethal challenges to President Obama’s landmark Affordable Care Act. A decision against the law could have left more than 6 million people without insurance coverage due to rising premiums that people could no longer afford.