This report describes invasive fungal infections in patients receiving Bruton tyrosine kinase inhibitors (BTKIs). A 75-year-old male with chronic lymphocytic leukemia on acalabrutinib presented with fever and cough. Imaging revealed pulmonary infiltrates, and bronchoalveolar lavage identified Aspergillus fumigatus, diagnosed as invasive pulmonary aspergillosis. He was successfully treated with isavuconazole. Another case involved a 66-year-old male with mantle cell lymphoma on acalabrutinib who developed rhinocerebral mucormycosis, confirmed by biopsy. This highlights BTKIs as a risk factor for severe invasive fungal infections like aspergillosis and mucormycosis. Teaching point: Clinicians should maintain a high index of suspicion for invasive fungal infections in BTKI-treated patients presenting with compatible symptoms.