Mucormycosis is a rare fungal infection caused by Mucorales order fungi. The rhino-cerebral form of mucormycosis is most commonly seen in patients with diabetes mellitus, whereas, pulmonary mucormycosis is a rare manifestation in patients with haematological malignancy and transplant recipients. We report a case of pulmonary mucormycosis presenting with a late acute onset diabetes on a patient immunosuppressed with a low dose of steroids. We aim to illustrate the need for a high clinical suspicion for the diagnosis of mucormycosis and to report the importance of early and aggressive inhiation of antifungal therapy.