We construct a Beurling generalized number system satisfying the Riemann hypothesis and whose integer counting function displays extremal oscillation in the following sense. The prime counting function of this number system satisfies π(x) = Li(x) + O(√ x), while its integer counting function satisfies the oscillation estimate N (x) = ρx + Ω ± x exp(−c √ log x log log x) for some c > 0, where ρ > 0 is its asymptotic density. The construction is inspired by a classical example of H. Bohr for optimality of the convexity bound for Dirichlet series, and combines saddle-point analysis with the Diamond-Montgomery-Vorhauer probabilistic method via random prime number system approximations.