A NLO QCD PDF fit analysis with simultaneous determination of the
strong coupling constant $\alpha_s(M_Z)$ is presented. The analysis is
based on the same combined H1 and ZEUS inclusive DIS measurements
as HERAPDF1.5 fit, together with jet measurements provided by both
H1 and ZEUS collaborations. The inclusion of jet data in the analysis
significantly reduces the correlation between the gluon parton density
function and the strong coupling, improving the precision of the gluon
PDF and providing an accurate determination of $\alpha_s(m_Z)$.