​I'll have a Big Mac, fries -- and a Monster energy drink

NEW YORK - McDonald's (MCD) says it's testing Monster energy drinks at about 20 restaurants in the U.S., the latest sign the chain is looking for ways to adapt to changing tastes.

"We're always gathering feedback from customers on the food and beverages they'd like to be served at McDonald's and this is another example," Lisa McComb, a McDonald's representative, said in an email.

Monster Beverage, a privately held company based in Corona, California, is known for its caffeinated energy drinks. McDonald's, which serves Coke fountain drinks at its more than 14,300 U.S. locations, didn't immediately specify which Monster drinks it's serving in the test. Last year, the fast-food chain's longtime beverage partner Coca-Cola (KO) struck a deal to buy a 17 percent stake in Monster.

The Monster drinks are being tested at locations in Florida, Georgia, Illinois, Michigan and Ohio, the company said Tuesday.

McDonald's, based in Oak Brook, Illinois, is trying to revive slumping sales in the U.S. by tweaking its food to improve the taste. The moves include toasting buns longer and searing meat differently to lock in the flavor.

Earlier this month, it also began making breakfast items like its Egg McMuffin available throughout the day.