A robotic surgical instrument comprising: a shaft; an articulation at a distal end of the shaft configured to articulate an end effector, the articulation driveable by a pair of driving elements; and an instrument interface at a proximal end of the shaft, the instrument interface comprising: an instrument interface element configured to drive the pair of driving elements, the instrument interface element displaceable over a displacement range, the pair of driving elements fast with the instrument interface element such that a displacement of the instrument interface element is transferred to the pair of driving elements; a tensioning mechanism configured to tension the pair of driving elements; and an alignment mechanism configured to set the displacement position of the instrument interface element to a predetermined alignment position when the end effector has a predetermined configuration, the alignment mechanism being independent of the tensioning mechanism.