  We revisit the simplest model of Higgs portal fermionic dark matter. The dark
matter in this scenario is thermally produced in the early universe due to the
interactions with the Higgs boson which is described by a non-renormalisable
dimension-5 operator. The dark matter-Higgs scattering amplitude grows as
$\propto \sqrt{s}$, signalling a breakdown of the effective description of the
Higgs-dark matter interactions at large enough (compared to the mass scale
$\Lambda$ of the dimention-5 operator) energies. Therefore, in order to
reliably compute Higgs-dark matter scattering cross sections, we employ the
K-matrix unitarisation procedure. To account for the desired dark matter
abundance, the unitarised theory requires appreaciably smaller $\Lambda$ than
the non-unitarised version, especially for dark matter masses around and below
the Higgs resonance, $m_{\chi}\lesssim 65$ GeV, and $m_{\chi}\gtrsim $ few TeV.
Consequently, we find that the pure scalar CP-conserving model is fully
excluded by current direct dark matter detection experiments.
