In April of 2010, five police officers put Michael Kingsley face down on a cement bunk in a holding cell, shocked him with a stun gun for five seconds, then left him alone, writhing in pain with his hands cuffed behind his back, for 15 minutes. Kingsley sued the officers, claiming they violated his constitutional rights by using excessive force. He lost.

On Monday, the Supreme Court gave Kingsley a second chance, ruling that the trial court gave the jury bad instructions. In a narrow sense, the decision turns on a technical question of intent. In a broader sense, though, the ruling is a blast of good news for opponents of police brutality—an emphatic declaration that the Constitution bars police from beating and abusing suspects in custody.

At the heart of Kingsley v. Hendrickson is a pretty straightforward question of intent. During the trial, the judge told the jury that Kingsley must lose unless he could prove the officers knew their actions could unduly harm Kingsley but went through with them anyway. Under that high standard, Kingsley lost. It’s incredibly difficult to prove law enforcement intentionally deprived suspects of their constitutional rights. Just ask the family of Michael Brown.

But Kingsley argued that he shouldn’t have to prove the officers were subjectively aware that their use of force was unreasonable. By forcing him to convince a jury that the officers had a malicious state of mind, Kingsley believed, the court made him clear too high a hurdle to vindicate his constitutional rights. Rather, Kingsley insisted that he should only have to prove that their use of force was objectively unreasonable to win his suit.

A bare majority of the Supreme Court agreed with Kingsley, sending the case back down to an appeals court to decide whether the error was so grave that Kingsley must be given a new trial. The dry majority opinion by Justice Stephen Breyer barely hints that the decision will have an impact beyond Kingsley’s case. But in reality, Kingsley constructs a crucial new constitutional protection against police abuse—a protection especially vital in the shadow of Freddie Gray’s shocking death.

Kingsley involves an application of one of the Constitution’s most fundamental provisions, the due process clause. (As the justices love to remind us, the concept of due process comes from the Magna Carta itself.) This clause bars the government—or any “state actor,” such as a police officer—from depriving “any person” of “life, liberty or property without due process of law.” Kingsley argues that the “liberty” protected by this clause includes the right to be free from unreasonable force while awaiting trial. Thus, when police officers held down and stunned Kingsley, they violated his constitutionally protected liberty with no semblance of due process.

It might seem obvious that the constitution protects pretrial detainees—who are, of course, innocent in the eyes of the law—from police abuse. But before Kingsley, it was not at all clear just how many constitutional protections pretrial detainees were afforded. The Eighth Amendment, which forbids “cruel and unusual punishment,” applies only to convicted prisoners. The Fourth Amendment’s protection against “unreasonable” police mistreatment seems to apply only to free people outside of prison. People like Kingsley—who have been arrested but not convicted and cannot make bail—fall into a hazy constitutional gray zone. As Justice Sonia Sotomayor noted during oral arguments, law enforcement seemed to want authority “to get a free kick in” when dealing with pretrial detainees:

Kingsley makes the gray zone a lot less dangerous. Under the decision, any “objectively unreasonable” use of force against detainees is unconstitutional. Just as importantly, the court reaffirmed that “pretrial detainees (unlike convicted prisoners) cannot be punished at all.” In other words, police cannot penalize a suspect, much less abuse him, merely because they believe he’s committed a crime.

Consider the Maryland police’s alleged maltreatment of Freddie Gray. As my colleague Jamelle Bouie explained, Gray’s arrest itself was probably an illegal violation of the Fourth Amendment. But once Gray was taken into police custody, only the 14^th Amendment’s due process clause protected him from abuse. Before Kingsley, Gray’s family might have had to prove that Gray’s alleged killers intentionally and knowingly severed his spinal cord if it hopes to sue them. Now, with Kingsley on the books, Gray’s family need only prove that the officers used objectively unreasonable force toward Kingsley in order to win a civil rights suit against them.

Writing in dissent, Justice Antonin Scalia accused the majority of being “tender-hearted” (which, to his mind, is a bad thing). But the rest of his opinion is strangely muted, as though even this famously law-and-order justice can’t work up the vigor to defend brutal police officers. Kingsley was the right decision in the right case at the right time. It won’t halt police overreach all at once. But it does send a powerful message that an individual’s constitutional rights are not revoked the moment he is put in handcuffs.