We present de Haas-van Alphen oscillation measurements showing a strong spin dependence of the quasiparticle mass enhancement in the heavy fermion superconductor CeCoIn5 at high magnetic fields. There is evidence that the Fermi-liquid temperature dependence of the oscillations, embodied in the Lifshitz-Kosevich equation, is breaking down on the most strongly renormalized Fermi surface sheets.