The K conversion coefficient of the 135.5 keV M4 transition in 193 rapt has been determined by the XPG method. The result is eK = 135.2 + 10.5 and the value exhibits a deviation 3.4 % below the theoretical prediction of Hager and Seltzer. Similar deviations have been systematically observed in precision values of E3 and M4 conversion coefficients reported in the literature.