  In recent years, there have been a growing number of observations indicating
the presence of rocky material in short-period orbits around white dwarfs. In
this Letter, we revisit the prospects for habitability around these
post-main-sequence star systems. In addition to the typically considered
radiative input luminosity, potentially habitable planets around white dwarfs
are also subjected to significant tidal heating. The combination of these two
heating sources can, for a narrow range of planetary properties and orbital
parameters, continuously maintain surface temperatures amenable for
habitability for planets around white dwarfs over time scales up to 10 Gyr. We
show that for a specific locus of orbital parameter space, tidal heating can
substantially extend the timescale of continuous habitability for a planet
around a white dwarf.
