  In the Minimal Supersymmetric Standard Model (MSSM) the mass of the lightest
neutral Higgs boson is determined by the supersymmetric parameters. In the
$m_h$MSSM the precisely measured Higgs boson replaces the trilinear coupling
$A_t$ as input parameter. Expressions are derived to extract $A_t$ in a
semi-analytical form as a function of the light Higgs boson (pole) mass. An
algorithm is developed and implemented at two--loop precision, generalizable to
higher orders, to perform this inversion consistently. The result of the
algorithm, implemented in the SuSpect spectrum calculator, is illustrated on a
parameter set compatible with LHC measurements.
