  In the present paper we prove a uniqueness theorem for the static and
asymptotically flat solutions to the Einstein-scalar field equations which
possess a photon sphere. We show that such solutions are uniquely specified by
their mass $M$ and scalar charge $q$ and that they are isometric to the
Janis-Newman-Winicour solution with the same mass and scalar charge subject to
the inequality $\frac{q^2}{M^2}<3$.
