  The Tibet AS$\gamma$ experiment provided the first measurement of the total
diffuse gamma-ray emission from the Galactic disk in the sub-PeV energy range.
Based on the analysis of TeV sources included in the HGPS catalog, we predict
the expected contribution of unresolved sources in the two angular windows of
the Galactic plane observed by Tibet AS$\gamma$. We show that the sum of this
additional diffuse component due to unresolved sources and the truly diffuse
emission, due to cosmic ray interaction with the interstellar medium, well
saturates the Tibet data, without the need to introduce a progressive hardening
of the cosmic-ray spectrum toward the Galactic center.
