If you or a loved one carries an EpiPen or EpiPen Jr. auto-injector for use in the case of a dangerous allergic reaction, check the device’s lot number. A subset of devices distributed between December 2015 and July 2016 have been voluntarily recalled in the United States after the manufacturer received two reports that EpiPens did not activate as intended.

The two problems were caused by a defective part that could potentially make the device difficult to activate in an emergency, the Food and Drug Administration reported on Friday. Both reports occurred outside the United States, and in both cases the EpiPen users were able to receive treatment from an alternative device.

The voluntary recall began in mid-March in Europe, Japan, Australia, and New Zealand, and has since expanded into North and South America and other parts of Asia. In the U.S., 13 separate lots—with expiration dates of April, May, September, and October 2017—are included in the recall.

People who have EpiPen or EpiPen Jr. devices can check the 2-pack cartons or the auto-injectors themselves for lot numbers and expiration dates. The lots affected in the United States are 5GM631, 5GM640, 6GM082, 6GM072, 6GM081, 6GM088, 6GM199, 6GM091, 6GM198, and 6GM087 (regular EpiPen, 0.3 mg), and 5GN767, 5GN773, and 6GN215 (EpiPen Jr., 0.15 mg).

Any auto-injectors from those lots should be replaced as soon as possible, says a statement from Mylan, EpiPen’s distributor. But don’t toss them before you get your hands on a new one: “We are asking patients to keep their existing product until their replacement product can be secured,” says Mylan’s statement.

Instead, consumers are encouraged to visit mylan.com/EpiPenRecall or call 877-650-3494 for further instructions. Starting today, Mylan says, consumers will begin receiving vouchers to trade in for new replacement products at their local pharmacies. They’ll also receive a container for mailing back back the recalled devices.

As a replacement, consumers can receive either EpiPen branded auto-injectors or Mylan’s authorized generic equivalent. (None of the currently recalled lots include the generic version.)

RELATED: 31 Everyday Things That Can Trigger Allergies

If your EpiPen is from a lot not included in the recall, it does not need to be replaced before its expiration date, says Christina Ciaccio, MD, assistant professor of pediatrics at the University of Chicago Medical Center. However, she does recommend keeping an eye on the list of affected products, in case the recall expands further.

And for anyone who relies on EpiPen and is spooked by the news, Dr. Ciaccio offers some words of reassurance. “Recalls on epinephrine auto-injectors have occurred in the past,” she says, “but overall, the reliability of these devices has been excellent. Companies that manufacture auto-injectors have done an excellent job moving quickly when a problem has been discovered.”

That being said, she adds, it is always a good idea to carry more than one auto-injector—for two reasons. “The first is in case the auto-injector misfires, either by user error or manufacturing error,” she says. “The second is in case he or she needs a second injection before arriving at the emergency department.”

To get more news you need to know delivered to your inbox, sign up for the Healthy Living newsletter

According to Mylan’s statement, both of the reports that prompted the recall occurred in a single lot, and the defect that was responsible for the failures is extremely rare. However, the statement continues, the recall has being expanded to include additional lots “as a precautionary measure out of an abundance of caution.”

The EpiPen has been in the news consistently over the last few months, after a report in August showed that the device’s price had skyrocketed by more than 600% since 2008. To save money, some patients and doctors even resorted to making their own pre-filled epinephrine syringes.

In the past few months, several new commercial products have hit the market, as well: Mylan now produces its own generic auto-injector at a lower price; CVS announced its own generic version called Adrenaclick; and the competing brand Auvi-Q recently returned to the market—with new and improved safety checks—after it was voluntarily recalled in 2015.

Dr. Ciaccio says that she and her colleagues are “very excited” that several options of epinephrine auto-injectors are now available for patients to choose from. “If EpiPen is not the right device for you or you have difficulty getting one after the recall,” she says, “try another, or even carry more than one brand.”