We include the new, five-loop, O(alpha_s^4) correction into the QCD
sum rule used for the s-quark mass determination. The pseudoscalar
Borel sum rule is taken as a study case. The OPE for the correlation
function with N^4LO, O(alpha_s^4) accuracy in the perturbative part,
and with dimension ⇐ 6 operators reveals a good convergence. We
observe a significant improvement of stability of the sum rule with
respect to the variation of the renormalization scale after including
the O(alpha_s^4) correction. We obtain the interval
m_s(2 GeV)=105 \pm 6 \pm 7 MeV, which exhibits about 2 MeV increase
of the central value, if the $O(alpha_s^4)
terms are removed.
