The production cross section of top-quark pairs associated with a photon tt + γ is determined in the muon+jets decay channel using 19.7 fb-1 of data taken at √s = 8 TeV with the CMS detector. The relative fraction of tt + γ events normalized to inclusive tt production is measured. Using an inclusive CMS cross section measurement, the tt + γ cross section is determined and found to agree with the standard model expectation.