A piston for attenuation of detonation in a combustion chamber in an internal combustion engine has a top wall accommodating a cap. The cap has an upwardly and inwardly inclined first section, a downwardly and inclined second section and a transverse wall at the inner end of the second section. The transverse wall projects upwardly from the top wall of the piston and extends across the piston in the direction of movement of the flame front in the combustion chamber. The first section has a plurality of channels providing paths for the flame front. The second section has an additional channel providing a further path for the flame front. The flame front commences at the ignition point moves over the cap and the transverse wall. The transverse wall provides an abrupt increase in the cross sectional areas of the combustion chamber in the direction of travel of flame front which attenuates detonation in the combustion chamber.