  We study the order $\alpha'$ correction to the string black hole found by
Garfinkle, Horowitz, and Strominger. We include all operators of dimension up
to four in the Lagrangian, and use the field redefinition technique which
facilitates the analysis. A mass correction, which is implied by the work of
Giddings, Polchinski, and Strominger, is found for the extremal GHS black hole.
