  In the presence of phase fluctuations the dc Josephson effect is modified and
the supercurrent at zero voltage is replaced by a peak at small but finite
voltages. It is shown that at zero temperature this peak is determined by two
complementary expansions of finite radius of convergence. The leading order
expressions are related to results known from the regimes of Coulomb blockade
and of macroscopic quantum tunneling. The peak positions and the suppression of
the critical current by quantum fluctuations are discussed.
