The fading characteristics of KCl:Eu2+(150 ppm) thermoluminescent crystals is determined. It is shown that the fading cannot be correctly measured without taking into account the phenomenon of self‐irradiation of the crystals, due to natural radioactive nuclide40K which is presented in potassium halide dosimeters. The results obtained can be useful in those applications of KCl: Eu2+crystals dealing with long‐time exposures, or low‐dose levels of radiation. ©1995 American Institute of Physics.