  We re-examine the properties of the high-velocity and extremely low mass
white dwarf LP 400-22 and its close companion. Based on an extended observation
timeline we determined a binary period of P= 1.01016 d, somewhat longer than
the previously published period, and a mass function f(M_2)= 0.180 M_solar
implying a mass for the companion M_2 > 0.41 M_solar. We also re-appraised the
mass and cooling age of the white dwarf using low-metallicity (Z=0.001)
evolutionary models appropriate for an old halo member, M_1 = 0.19 M_solar and
t_cool~1.8 Gyr, and we infer a mass of 0.85 - 1.0 M_solar for the progenitor of
the white dwarf. We discuss the likely origin of this system.
