The invention relates to a glow plug for a diesel engine, said glow plug comprising a ceramic glow pencil, which has a heating portion, and a housing, from which the glow pencil protrudes, wherein the glow pencil has a ceramic inner conductor, an insulation layer surrounding the inner conductor, and a ceramic outer conductor layer arranged on the insulation layer. In accordance with this disclosure, the outer conductor layer in the heating portion only partially covers the insulation layer.