Vampire Weekend may not “give a f— about an Oxford comma,” but I certainly do. And so, too, does the United States Court of Appeals for the First Circuit, which opened a recent opinion, in a class action lawsuit about overtime pay for a dairy company’s delivery drivers, with these words:

“For want of a comma, we have this case.”

Also known as the serial comma, the Oxford comma is the comma after the second-to-last item in a list of three or more things. It is, in other words, the comma that precedes the words “and” or “or.”

Grammar and punctuation nerds have long been divided on the merits of the Oxford comma, which is common in book and academic publishing. Proponents point to the fact that the Oxford comma adds clarity and aids in comprehension. Yet there are detractors who consider the Oxford comma unnecessary. For stylistic reasons, many American news organizations, such as the Associated Press, omit the Oxford comma unless the omission would lead to confusion.

Omitting an Oxford comma can lead to humorous results. Here are just a few examples:

With:

“She took a photograph of her parents, the president, and the vice president.”

Without:

“She took a photograph of her parents, the president and the vice president.”

With:

“This book is dedicated to my parents, Ayn Rand, and God.”

Without:

“This book is dedicated to my parents, Ayn Rand and God.”

The First Circuit case, O’Connor v. Oakhurst Dairy, __ F.3d __ (1st Cir. 2017) (Case No. 16-1901), turned on a Maine statute that provides an exemption to otherwise required overtime pay for employees whose work involves the handling of certain expressly enumerated food products. Under the exemption, all of the following are exempt from 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.

If the statute had included a comma between the words “shipment” and “or distribution,” these activities would clearly have been a continuation of the list of activities exempt from overtime pay. The drivers argued that, without the comma, they were entitled to overtime pay for “distribution” because the statutory exemption did not include that activity. The dairy company, of course, argued that “distribution” was merely one of the activities on the list of overtime exemptions, regardless of the missing comma.

The Court agreed with the drivers, concluding that the absence of a comma created an ambiguity: “[i]f the exemption used a serial comma to mark off the last of the activities that it lists, then the exemption would clearly encompass an activity that the drivers perform.” And despite the fact Maine’s legislative style guide counsels against the Oxford comma, the Court held that the ambiguity of the exemption must be construed liberally to effectuate the legislative intent of the remedial statute—to provide overtime pay protection to employees—and thus agreed with the drivers’ narrower reading of the exemption.

Oxford commas may well be unnecessary in certain circumstances, but they do not create confusion. And as O’Connor shows, omitting that single keystroke can be surprisingly costly. Those who omit the Oxford comma live dangerously.