Both the soft (Maccacaro et al., 1982; Gioia et al., 1984; Giacconi et al., 1979; Griffiths et al., 1983) and the hard (Piccinotti et al., 1982) X-ray surveys provide crucial information on the evolution of AGNs in the X-ray band. Before combining the two data sets, however, the consistency of the two flux scales must be checked. To this end we have compared the soft (SX) and the hard (HX) X-ray luminosities of all powerful (log(SX)>43.5) AGNs for which both IPC and hard X-ray fluxes are available in the literature (lower luminosity objects frequently exhibit large intrinsic, luminosity dependent, absorbing columns which cannot be accurately accounted for). We find <log(HX)/(SX)> = 0.17±0.06, to be compared with the expected value <log(HX)/(SX)>≃0 for a typical X-ray energy index α X≃0.7. Thus, an average correction factor of ≃1.5 needs to be applied to the IPC fluxes to bring them into the hard X-ray flux scale.