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We reanalyze archival EAS-MSU data in order to search for events withanomalously low content of muons with energies E_mu>10 GeV in extensive airshowers with number of particles N_e>2*10^7. We confirm the first evidence fornonzero flux of primary cosmic gamma rays at energies E~10^17 eV. The estimatedfraction of primary gamma rays in the flux of cosmic particles with energiesE>5.4*10^16 eV is (0.43 +0.12-0.11)%, which corresponds to the intensity of(1.2 +0.4-0.3)*10^{-16} cm^{-2} s^{-1} sr^{-1}. The study of arrival directionsdoes not favour any particular mechanism of the origin of the photon-likeevents.Comment: 20 pages, 12 figures. V2: important misprints corrected (there was a  mismatch in numbers between the abstract and the main text, sorry). Version  to appear in JETP in December 201

Estimate of the fraction of primary photons in the cosmic-ray flux at energies ∼1017 eV from the EAS-MSU experiment data