A Converse Mean-Value Property

We prove a converse mean-value theorem for harmonic functions associated with the invariant Laplace–Beltrami operator on the real unit ball. Under suitable integrability and topological assumptions on the domain and its Green potential, we show that the invariant volume mean-value property characterizes hyperbolic balls centered at the origin. As a consequence, we also answer a question left open by Bruna and Détraz in the setting of invariantly harmonic functions.