  We report a frequency measurement of the 1S0-3P0 transition of 87Sr atoms in
an optical lattice clock. The frequency is determined to be 429 228 004 229 879
(5) Hz with a fractional uncertainty that is comparable to state-of-the-art
optical clocks with neutral atoms in free fall. Two previous measurements of
this transition were found to disagree by about 2x10^{-13}, i.e. almost four
times the combined error bar, instilling doubt on the potential of optical
lattice clocks to perform at a high accuracy level. In perfect agreement with
one of these two values, our measurement essentially dissipates this doubt.
