Using relativistic quantum mechanics, we study the spectrum of a non-BPS two-particle bound state in the massive phase of N = 4 super Yang-Mills, in the limit when one of the particles is infinitely heavier than the other. We find that the spectrum shows the exact n 2 degeneracy for each principal quantum number n, just as in the strict nonrelativistic limit. This is in line with the findings of Caron-Huot and Henn, who studied the same system in the large N limit with the technique of integrability and the dual conformal symmetry.