The FreeStyle Libre (Abbott) is a human continuous glucose monitor sensor that has been used to monitor glucose concentrations in dogs and cats with diabetes. This sensor and other similar continuous glucose monitoring sensors are increasingly popular in veterinary medicine, specifically for management of diabetes mellitus. The sensor decreases veterinary visits and reduces the stress (and expense) of multiple blood sample collections needed to produce glucose curves. However, there are no established guidelines for sensor placement in small animals and, to date, no substantial complications have been reported. A 15-year-old neutered male cairn terrier dog with a history of diabetes and suspected inflammatory bowel disease with progressive weight loss was presented with acute dyspnea <24 h after placement of a FreeStyle Libre 2 sensor. He was diagnosed with a continuous pneumothorax suspected secondary to a FreeStyle Libre 2 sensor placement. Multiple thoracocenteses were completed but further treatment was declined, and the dog was euthanized. Key clinical message: This case highlights the importance of sensor placement selection, especially in small animals, and documents the first reported pneumothorax suspected to be secondary to a continuous glucose monitor placement. This specific complication has apparently not been documented previously.