We present light curves of SDSS J0926+3624, the first eclipsing AM CVn star, observed with the high-speed CCD camera ULTRACAM on the WHT. We find, unusually, that the accreting white dwarf is only partially eclipsed by its companion. Apart from this, the system shows the classic eclipse morphology displayed by eclipsing dwarf novae, namely the eclipse of a white dwarf and accretion disc followed by that of the bright spot where the mass transfer stream hits the disc. We are able to fit this well to find masses of the accretor and donor to be M_1 = 0.84 ± 0.05 M_☉ and M_2 = 0.029 ± 0.02 M_☉ respectively. The mass of the donor is significantly above its zero temperature value and it must possess significant thermal content.