Nucleic acids encoding Parvoviral Rep proteins with a mutated nuclear localization signal (NLS) are provided. Also provided is a nucleic acid comprising a nucleotide sequence encoding a Parvoviral Rep protein with a mutated zinc finger domain and a nucleic acid comprising a nucleotide sequence encoding a Parvoviral Rep protein comprising an amino acid mutation at position 43, 57, 79, 97, 120, 179, 305, 484, 493 or 571 with reference to SEQ ID NO: 2. Nucleic acid constructs and cells, such as insect cells, comprising the nucleic acids are provided as well as a method for producing a recombinant Parvoviral virion using the nucleic acids.