We present a case of probable invasive pulmonary aspergillosis due to Aspergillus flavus, in a female patient treated for an acute myeloid leukemia. Two weeks after an allogenic stem cell transplantation a probable invasive pulmonary aspergillosis was diagnosed based on thoracic imaging combined with positive galactomannan antigen and positive in-house mitochondrial Aspergillus qPCR in serum. Although an antifungal treatment was initiated, Aspergillus qPCR and galactomannan antigen remained positive in serum and worsening of the thoracic lesions was observed. The discordance between the negativity of the in-house ribosomal Aspergillus qPCR (specific to A. fumigatus) and the positivity of the in-house mitochondrial Aspergillus qPCR (targeting A. fumigatus and some other Aspergillus) allowed the suspicion of a thermophilic Aspergillus species that was not A. fumigatus. No strain was obtained in culture but the involvement of A. flavus was confirmed using a specific A. flavus qPCR. This case illustrated the usefulness of our original strategy combining two different in-house Aspergillus qPCRs, in addition to galactomannan assay, to diagnose invasive aspergillosis in hematology patients.