A glow plug adaptor for pressure measurement in a combustion chamber of an internal combustion engine includes an adaptor sleeve attached to an adaptor head that contains a pressure sensor with a diaphragm. A sealing shoulder can be screwed into an opening in a combustion chamber to provide a pressure-tight seal and permit passage of signal conductors from the pressure sensor through the adaptor sleeve. The adaptor head is tapered at the proximal combustion chamber end, and in the adaptor head a cavity is formed in such a way that the cavity is bounded by the diaphragm of the pressure sensor mounted therein and by a closed end wall of the adaptor head.