We report on a two-loop supersymmetric contribution to the magnetic moment (g − 2)μ of the muon which is enhanced by two powers of tan β. This contribution arises from a shift in the relation between the muon mass and Yukawa coupling and can increase the supersymmetric contribution to (g − 2)μ sizably. As a result, if the currently observed 3σ deviation between the experimental and SM theory value of (g − 2)μ is analyzed within the Minimal Supersymmetric Standard Model (MSSM), the derived constraints on the parameter space are modified significantly: If (g − 2)μ is used to determine tan β as a function of the other MSSM parameters, our corrections decrease tan β by roughly 10% for tan β = 50.