We compute an explicit presentation of the (topological) automorphism group of a particular Toeplitz subshift with subquadratic complexity. The automorphism group is a non-finitely generated subgroup of rational numbers, or alternatively the 5-adic integers, under addition, the shift map corresponding to the rational number 1. The group is ( (5/2) i | i ∈ N , +) ≤ (Q, +).