  Previous timing data for PSR~B1620$-$26 were consistent with a second
companion mass $m_2$ anywhere in the range $\sim10^{-3}-1\,M_\odot$, i.e., from
a Jupiter-type planet to a star. We present the latest timing parameters for
the system, including a significant change in the projected semi-major axis of
the inner binary, a marginal detection of the fourth time derivative of the
pulse frequency, and the pulsar proper motion (which is in agreement with
published values for the proper motion of M4), and use them to further
constrain the mass $m_2$ and the orbital parameters. Using the observed value
of $\stackrel{\ldots.}{f}$, we obtain a one-parameter family of solutions, all
with $m_2 \lo 10^{-2}\,M_\odot$, i.e., excluding stellar masses. Varying
$\stackrel{\ldots.}{f}$ within its formal $1\sigma$ error bar does not affect
the mass range significantly. However, if we vary $\stackrel{\ldots.}{f}$
within a $4\sigma$ error bar, we find that stellar-mass solutions are still
possible. We also calculate the predicted rate of change of the projected
semi-major axis of the inner binary and show that it agrees with the measured
value.
