The detection of galactomannan (GM) in the serum of in immunocompromised patients is widely used for the early diagnosis of invasive aspergillosis. We report a case of a false-positive GM test presumably caused by the enteral nutritional supplement given to a non-neutropenic patient with intestinal graft-versus-host disease after a hematopoietic stem cell transplant. Clinicians should be alert to the possibility of false-positive GM results in patients on nutritional supplements.