  In 2011, Bailes et al. reported on the discovery of a detached companion in a
131 minute orbit around PSR J1719-1438, a 173 Hz millisecond pulsar. The
combination of the very low mass function and such a short orbital period is
unique. The discoverers suggested that the progenitor system could be an
ultracompact X-ray binary (UCXB), which is a binary with a sub-hour orbital
period in which a (semi-)degenerate donor fills its Roche lobe and transfers
mass to a neutron star. The standard gravitational-wave driven UCXB scenario,
however, cannot produce a system like PSR J1719-1438 as it would take longer
than the age of the Universe to reach an orbital period of 131 min. We
investigate two modifications to the standard UCXB evolution that may resolve
this discrepancy. The first involves significant heating and bloating of the
donor by pulsar irradiation, and in the second modification the system loses
orbital angular momentum via a fast stellar wind from the irradiated donor,
additional to the losses via the usual gravitational wave radiation. In
particular a donor wind is effective in accelerating orbital expansion, and
even a mild wind could produce the 131 minute period within the age of the
Universe. We note that UCXBs could be an important class of progenitors of
solitary millisecond radio pulsars.
