A Maine court ruling in a case about overtime pay and dairy delivery didn’t come down to trucks, milk, or money. Instead, it hinged on one missing comma.

Delivery drivers for local milk and cream company Oakhurst Dairy have been tussling with their employers over whether they qualify for overtime. On March 13, a US court of appeals determined that certain clauses of Maine’s overtime laws are grammatically ambiguous. Because of that lack of clarity, the five drivers won their appeal and were found eligible for overtime. The case now can be heard in a lower court.

The profoundly nerdy ruling is also a win for anyone who dogmatically defends the serial comma.

The serial comma, also known as the Oxford comma for its endorsement by the Oxford University Press style rulebook, is a comma used just before the coordinating conjunction (“and,” or “or,” for example) when three or more terms are listed. You’ll see it in the first sentence of this story—it’s the comma after “milk”—but you won’t find it in the Maine overtime rule at issue in the Oakhurst Dairy case. According to state law, the following types of activities are among those that don’t qualify for overtime pay:

The canning, processing, preserving,

freezing, drying, marketing, storing,

packing for shipment or distribution of:

(1) Agricultural produce;

(2) Meat and fish products; and

(3) Perishable foods.

There, in the comma-less space between the words ”shipment” and “or,” the fate of Kevin O’Connor v. Oakhurst Dairy was argued. Is packing (for shipment or distribution) a single activity that is exempt from overtime pay? Or are packing and distributing two different activities, and both exempt?

If lawmakers had used a serial comma, it would have been clear that distribution was an overtime-exempt activity on its own. But without the comma, wrote US appeals judge David J. Barron, the law is ambiguous as to whether distribution is a separate activity, or whether the whole last clause—”packing for shipment or distribution”—is one activity, meaning only the people who pack the dairy products are exempt. The drivers do distribute, but do not pack, the perishable food.

The debate over the serial comma has long raged and remains unresolved. Proponents of its use (like Quartz, which breaks with the AP Stylebook on this vital matter) say that, when listing things in writing, a comma before the last item is paramount. It separates the sentence “He ate dessert, fries, and ham” from “He ate dessert, fries and ham.” Opponents say that it’s redundant, aesthetically displeasing, and potentially more ambiguous.

Oakhurst, for its part, had argued that “distribution” was separate in the language of the law, meaning its drivers did not qualify for overtime.

In an impressively geeky retort, the drivers responded that all the other exempted activities were listed as gerunds, words ending with “-ing”: Canning, processing, preserving, freezing, drying, marketing, storing, packing. The word “distribution,” they argued, was therefore not intended to be one of the items in the list.

The first court to hear the case ruled in the company’s favor, but the appellate court disagreed. Wrote Barron, since Maine’s overtime laws are meant to have ”remedial purpose,” that is, to help the state’s workers, they should be read liberally. He and the appeals court therefore sided with the drivers, ruling that they are still eligible to receive their unpaid overtime.

Maine has a style guide for legislation, and Oakhurst had argued it expressly instructs law-writers not to use the serial comma:

Do not write: Write: Trailers, semitrailers, and pole trailers Trailers, semitrailers and pole trailers

But, as the appeals court argues—and the style guide shows—clarity is of the utmost importance when a list is ambiguous. From the appellate court ruling:

The manual also contains a proviso—”Be careful if an item in the series is modified”—and then sets out several examples of how lists with modified or otherwise complex terms should be written to avoid the ambiguity that a missing serial comma would otherwise create.

Correction, March 16: An earlier version of this article stated that the five drivers won their lawsuit against Oakhurst. At time of writing, they had won the appeal, not the lawsuit.