  We investigate the production of the gamma-ray spectrum of a Poynting-flux
dominated GRB ouflow. The very high magnetic field strengths
(super-equipartition) in such a flow lead to very efficient synchrotron
emission. In contrast with internal shocks, dissipation of magnetic energy by
reconnection is gradual and does not produce the spectrum of cooling electrons
associated with shock acceleration.We show that a spectrum with a break in the
BATSE energy range is produced, instead, if the magnetic dissipation heats a
small (\sim 10^{-4}) population of electrons.
