A method of detecting a shaft break in a turbine engine is provided. The shaft connects a torque-exerting turbine of the engine to a torque-receiving unit of the engine. The method includes: receiving repeated measurements of the rotational frequency of the torque-receiving unit and the rotational frequency measurements of the turbine; determining from the measurements an amount of shaft twist between the turbine and the torque-receiving unit; comparing the amount of twist with a threshold twist value; and signalling a shaft break when the amount of twist exceeds the threshold twist value and a pre-condition is met. The pre-condition includes determining from the measurements that the turbine rotational speed is greater than the simultaneous torque-receiving unit rotational speed by a threshold speed value.