The present invention relates to mutant MVA vaccinia viruses, which are used for the generation of recombinant MVA viruses, as well as host cells, which have been infected with these mutant MVA viruses. The present invention further relates to DNA-vector constructs, and a method for the generation of recombinant MVA by using the mutant MVA viruses and the DNA-vector constructs. The mutant MVA vaccinia viruses of the present invention are characterized in that the MVA ORF 050L gene or a functional part thereof has been inactivated in the viral genome.