An internal combustion engine having: a housing with at least one cylinder and a pre-chamber spark plug; the cylinder has a piston that is able to move in the housing and delimits a combustion chamber contained in the housing; the combustion chamber has a compressed volume when the piston is at top dead center; the pre-chamber spark plug has a body, an external thread at its front end, a passage, an insulator positioned in the passage, a center electrode protruding from the front end of the insulator, and a pre-chamber-forming cap that is placed at the front end of the body and delimits a pre-chamber. The cap shields the center electrode from the combustion chamber and has at least one opening, which enables a gas exchange between the pre-chamber and the combustion chamber. In one embodiment, the total volume of the pre-chamber makes up at least 0.65% of the compressed volume of the combustion chamber.