  Observations performed with the Fermi-LAT telescope have revealed the
presence of a spectral break in the GeV spectrum of flat-spectrum radio quasars
(FSRQs) and other low- and intermediate-synchrotron peaked blazars. We propose
that this feature can be explained by Compton scattering of broad-line region
(BLR) photons by a non-thermal population of electrons described by a
log-parabolic function. We consider in particular a scenario in which the
energy densities of particles, magnetic field, and soft photons in the emitting
region are close to equipartition. We show that this model can satisfactorily
account for the overall spectral energy distribution of the FSRQ 3C 454.3,
reproducing the GeV spectal cutoff due to Klein-Nishina effects and a curving
electron distribution.
