The present invention relates to methods for producing a polypeptide of interest by (a) cultivating a mutant of a parent Aspergillus cell, wherein (i) the mutant comprises a first nucleic acid sequence encoding the polypeptide and a second nucleic acid sequence comprising a modification of at least one of the genes responsible for the biosynthesis or secretion of at least one toxin, and (ii) the mutant produces less of the toxin than the parent Aspergillus cell when cultured under the same conditions; and (b) isolating the polypeptide from the culture medium. Also, mutants of Aspergillus cells are provided, as well as methods for obtaining the mutant cells.