Applying results on linear forms in p-adic logarithms, we prove that if (x, y, z) is a positive integer solution to the equation x y − y x = c z with gcd(x, y) = 1 then (x, y, z) = (2, 1, k), (3, 2, k), k ≥ 1 if c = 1, and either (x, y, z) = (c k + 1, 1, k), k ≥ 1 or 2 ≤ x < y ≤ max{1.5 × 10 10 , c} if c ≥ 2.