If a police officer arrests someone in retaliation for protected speech, it’s a First Amendment violation. But suppose that apart from the speech, there was probable cause to arrest that person for a crime? Lower courts have long disagreed whether such a person could bring a claim alleging a First Amendment retaliatory arrest. Twice in the last decade, the U.S. Supreme Court has taken a case to resolve the issue, only to punt and decide the case on other grounds. This year, in Nieves v. Bartlett, the third time proved to be the charm. In an opinion written by Chief Justice Roberts, the Court set out a standard for First Amendment retaliatory arrest claims.

Nieves arose from Alaska’s “Arctic Man” festival, which the Court noted is “known both for extreme sports and extreme alcohol consumption.” Nieves was arrested there for disorderly conduct. The arresting officers said it was because Nieves was too drunk and obnoxious—even by “Arctic Man” standards—and was interfering with their investigation of underage drinking. But Nieves claimed that the officers had arrested him in retaliation for anti-police comments earlier that day.

A strong majority of the Supreme Court (both “liberal” and “conservative” justices) held that because there was objective probable cause to arrest Nieves, his First Amendment retaliation claim failed. The Court made two main points. One, in retaliation cases, the plaintiff must always show that the retaliatory act would not have happened but for the protected activity. But if there is objective probable cause to justify an arrest, the plaintiff cannot meet that causation burden. Two, under longstanding Fourth Amendment principles, the constitutionality of an arrest turns on whether there was objective probable cause for the arrest, not the arresting officer’s motivations. The Court saw no reason to create a special exception to that principle—with one notable caveat.

The caveat was that if other people were engaging in the same conduct for which the plaintiff was arrested, minus the protected speech, and were not arrested, the First Amendment Retaliation claim survives. The Court gave the example of a city street where many people were jaywalking at an intersection, but the only person arrested for jaywalking was the one person engaged in a political protest. That person could bring a retaliatory arrest claim, because the causation analysis would be different and because the claim’s validity would still turn on objective evidence of differential treatment, not subjective motivations.

The Court’s ruling is a qualified win for law enforcement. Officers now have less reason to fear that objectively valid arrests give rise to a suit based on what the Court described as “easy to allege and hard to disprove” claims about the officer’s state of mind. But officers, and municipalities training them, should also keep in mind the Court’s exception when considering whether to arrest a person who has made some kind of protected speech and ensure they are not singling out that person for arrest, because such conduct could give rise to liability.