A casing component (2) of a turbomachine, the casing component (2) comprising: a plurality of casing elements (14) which define a diameter of the casing component; and an actuation means operable to change the diameter of the casing component (2), wherein the actuation means changes the diameter of the casing component (2) as a function of a rotational speed of a rotatable component (4) disposed within the casing component (2).