This time of year, there are many opportunities to indulge in a flute of champagne or a tumbler of spiked eggnog. But if you’re trying to pace yourself — let’s say, at the office holiday party — you might want to bring your own glass.

It’s been well established that people have a hard time determining if there is more liquid in a short, wide glass than a tall, narrow one. Even if there’s an equal amount in both, we tend to use height to judge quantity, so people usually think there’s more in the tall glass. As a result, they usually end up pouring more into the short glass.

If that wasn’t enough to complicate happy hour, a new study finds that the shape of the glass also determines how quickly we consume alcohol.

Psychology researchers at the University of Bristol observed 160 social drinkers aged 18 to 40 with no history of alcoholism. The researchers found that their subjects finished a beer almost twice as fast when drinking from a curvy glass than from a straight-sided glass.

The researchers hypothesize that curves make it harder for drinkers to judge exactly how much they’ve consumed. We rely on visual cues to tell us how much we’ve had to drink, but shaped glassed can play tricks on our eyes. Even determining the halfway point in a curved glass can be difficult. Consequently, we may underestimate how much alcohol we’ve actually had to drink.

However, when the beverage was non-alcoholic, the study found that the shape of the glass had no impact on the speed of consumption. The researchers speculate that we only attempt to pace ourselves when drinking alcohol.

So drink responsibly this holiday season, preferably out of a tall, straight glass. Who knows? It may be enough to keep you on Santa’s — and your boss’s — “nice list.”