A simple solution for the uniqueness problem of the wave superposition method is proposed in this paper. Many authors have pointed out the discrete set of wavenumbers for which the solution of the underlying integral equations is not unique. So far, the usual solutions are theoretically sophisticated and/or numerically disadvantageous. Here, by adding some sources interior to the virtual surface defined by the wave superposition method, the uniqueness problem can be easily removed with low computational effort. Furthermore, dealing with simple monopoles, this method is well-suited for practical applications.