With the notable exception of same-sex marriage, the past few years have not been good ones for civil rights at the Supreme Court. The Voting Rights Act, women’s rights to health insurance, and, perhaps, the Fair Housing Act have all been severely weakened.

That’s why today’s decision strengthening the Pregnancy Discrimination Act, Young v. United Parcel Service, is a welcome reprieve. And what’s most notable about the Young opinion is who voted for what.

This was not a typical, liberal-versus-conservative split. The majority consisted of Chief Justice Roberts, and Justices Breyer, Ginsberg, Sotomayor and Alito—the liberals, yes, but joined by two conservatives.

The facts of the case are simple, but the law is not. UPS driver Peggy Young became pregnant, and was told by her doctor not to lift heavy packages. UPS refused to reassign her or let co-workers help her, and so she ended up losing months of pay. To add insult to injury, her employer cut off her medical coverage as well.

According to Young, UPS’s failure to accommodate her pregnancy was illegal. UPS has a policy of accommodating other people who temporarily can’t do heavy lifting, and refusing to do so for her was discrimination.

According to UPS, those other assignments were only in very specific cases, like on-the-job injury. Usually, they don’t accommodate employees who can’t do their jobs for physical reasons. (For example, think of an employee injuring her back playing basketball.) This wasn’t discrimination, they said, but neutrality.

Ultimately, the Court sided with Young, by a 6-3 margin. The legal reasoning is complex. Interestingly, the opinion by Justice Breyer rejected both Young’s and UPS’s readings of the Pregnancy Discrimination Act, but said that if an employer accommodates some temporary disabilities, it has to accommodate pregnancy. The employer needn’t put up with anything—the injured basketball player is still out of luck—but because of the PDA, it can’t treat pregnancy worse than it treats other temporary disabilities.

Perhaps most importantly, the Court’s opinion allows pregnant women to prove discrimination even absent a “smoking gun” if there is a pattern of unequal treatment. If Young can show that UPS accommodates some disabilities but not pregnancy, she wins—no matter how much UPS says they aren’t being discriminatory.

This process “to show disparate treatment through indirect evidence” is crucial, not just in PDA cases, but in all sorts of civil rights cases. Often, it’s difficult to show discriminatory intent. You’d have to find the memo with racist or sexist language, or the obviously outrageous employment policy. Those cases rarely even make it to court.

But the Supreme Court has been reluctant to expand “disparate treatment” jurisprudence, as well as its close relation “disparate impact.” Disparate impact is a central issue in this year’s challenge to the Fair Housing Act, for example, with Justice Scalia stating clearly that “racial disparity is not racial discrimination,” while at the same time noting that disparate impact theory is, by now, part of the settled law. (The decision in that case is expected soon.)

So why expand that reasoning here?

The reason is the literal text of the PDA itself. Justice Alito’s concurring opinion makes it clear that the PDA has a “further requirement of equal treatment irrespective of intent.” The PDA has two relevant clauses. While the first prohibits discrimination, the second has broader language that women must be “treated the same for all employment-related purposes… as other persons not so affected but similar in their ability or inability to work.”

For Justice Alito, even more so than for Justice Breyer’s opinion, that “treatment” language is dispositive. Indeed, if one wanted to read the Supreme Court tea leaves, it’s possible that Justice Alito wrote separately in order to distinguish the PDA from other statutes. This is pure speculation, but one could read him as saying “The PDA has special language in it—but without that special language, there’s no such thing as disparate treatment or disparate impact.”

In other words, the swing votes here, Chief Justice Roberts and Justice Alito, may have voted for a liberal social policy because of a conservative method of statutory interpretation. Yes, the end result is to expand the social safety net for women. But the reason that result was reached was because of a close, conservative reading of the statute in question.

For the record, Justice Scalia wrote his thousandth-or-so blistering dissent, full of the bluster that has characterized his decades on the court. He called the majority opinion “inventiveness posing as scholarship—which gives us an interpretation that is as dubious in principle as it is senseless in practice.” Zing.

Indeed, Justice Scalia’s contempt—his opinion includes the phrases “the fun does not stop there” and “(believe it or not) it gets worse” as well as multiple invocations of the exclamation “Poof!”—appears to have motivated Justice Kennedy to write his separate opinion, agreeing with Scalia’s reasoning but reminding us all that pregnancy and discrimination are both serious things.

For Peggy Young, her case now goes to trial, to establish the facts regarding UPS’s accommodations of others, and their refusal to accommodate her.

For women who want to keep their jobs, even if they become pregnant, Young v. UPS is clearly a step forward. As Justice Scalia’s dissent indicates, it could easily have gone the other way. But Young stands for the principle that, according to a literal reading of the Pregnancy Disability Act, if some disabilities are accommodated, pregnancy must be accommodated.

As such, the case is a win for social progressives—for largely conservative reasons.