We demonstrate a technique, which significantly enhances the stability of copper welding with laser radiation. After modelling spot welding stability we conclude that oxide layer morphology typical for native oxide layers has to be avoided. We locally normalize the surface oxidation degree using laser pulses in the nanosecond pulse duration regime (short prepulsing). Thereby, the absorptivity is reliably increased, setting uniform starting conditions for laser welding. A process window is identified, where all experimental repetitions lead to successful welds. With prepulsing, the spot weld diameter variation is decreased to 2\% and the necessary welding energy is decreased up to 40\%.