A four-stroke internal combustion engine (1) including variable compression ratio comprises a crankcase including at least a cylinder having an intake valve and an exhaust valve, a crankshaft (2) having a crankpin (4) and being supported by the crankcase and rotatable with respect thereto about a crankshaft axis (5), a connecting rod (9) including a big end (8) and a small end (10), a piston (11) being rotatably connected to the small (10) end and slidable in the cylinder, a crank member (6) being rotatably mounted on the crankpin (4), and comprising at least a bearing portion (7) which is eccentrically disposed with respect to the crankpin (4), and having an outer circumferential wall which bears the big end (8) of the connecting rod (9) such that the connecting rod (9) is rotatably mounted on the bearing portion (7) of the crank member (6) via the big end (8), a crank member drive system (12, 13, 14, 16) for rotating the crank member (6) at a rotation frequency with respect to the crankcase which is half of that of the crankshaft (2), and a control system (18-25) for operating the engine (1) with repetitive cycles, wherein each cycle includes an intake stroke, compression stroke, combustion stroke and exhaust stroke, respectively, and for changing the compression ratio in the compression stroke. The control system (18-25) is adapted such that it can interrupt the repetitive cycles by rotating the crankshaft (2) an additional single revolution between two successive combustion strokes for switching between a high and low compression ratio.