Version: kwant.__version__ == '1.0.0' Problem: when kwant.plotter.map() is given the axes to plot on such as kwant.plotter.plot(system, stuff_to_plot, ax = gca()) kwant/plotter.py first sets fig=None in line 1523 and the tries to create colorbar for a None object in line 1536 Possible solution: Either disable colorbar in this case line 1535: if colorbar and fig is not None: Or figure out how to create another axes with colorbar.