During myogenesis, multinucleate muscle fibers arise from the fusion of single nucleate myoblasts. In Drosophila, myoblast fusion is initiated by a specific kind of myoblast called founder cells (FCs), which determine the differentiation program for the nascent muscle fibers. Much of the information about muscle fusion and general muscle development is obtained via a toolkit of genetic drivers that are used to manipulate gene expression in a cell-specific manner. Typically, genetic drivers express the yeast transcriptional factor Gal4 to activate expression from artificial transgenic constructs containing Gal4-responsive upstream activating sequence (UAS). rP298 is a FC-specific genetic driver, but its practical use is very limited because it quickly becomes inactive upon the first fusion between FCs and myoblasts. We demonstrate that by adding a self-activating transgene UAS-Gal4 to rP298, it is possible to prolong Gal4 expression beyond myoblast fusion, into more advanced developmental stages including the adulthood. The idea is that Gal4, once initiated by rP298, activates itself though the UAS promoter and maintains continuous Gal4 expression. Thus, by allowing the Gal4 gene to maintain expression in post-fused muscle fibers, we now can study those regulatory genes that only become activated in FCs and which are likely to control the muscle differentiation program.