Medtronic (NYSE:MDT) is warning patients who use its MiniMed 600 series insulin pumps of an issue that could cause a dangerous over- or under-dosing of insulin.

In a letter to patients, the company said that the pump’s insulin reservoir may become loose if a retainer ring breaks, preventing a proper lock. Dropping the pump or bumping it on a hard surface may break that ring, the company said. If the reservoir is not properly locked into the pump, it could lead to over- or under-delivery of insulin, which could then result in hypoglycemia or hyperglycemia. The recall covers MiniMed 630G  (model MMT-1715) and MiniMed 670G (model MMT-1780).

A company spokesperson told the StarTribune of Minneapolis that Medtronic had received one report of a patient being hospitalized due to a retainer-ring issue, and one report of a death which may have been associated with the issue.

Medtronic advised patients to stop using the device if  the reservoir does not lock into the pump or if the is loose, damaged or missing. The company also said patients who drop or bump their pumps should examine the retainer ring and check that the reservoir locks properly. All patients should routinely check the retainer ring and check that your reservoir locks in place at every set change, the company added.

The company also said it had notified the FDA of the issue. Medtronic did not immediately respond to a request for comment on the recall.

Medtronic’s MiniMed 670G system is designed to automatically track and adjust a patient’s blood sugar levels by measuring blood glucose every few minutes and automating the dosing of insulin. The automated insulin delivery system first won FDA approval in September 2016. The FDA approved the MiniMed 630G in 2017.

MDT shares were up 0.53% to $111.06 in mid-morning trading.