An actuator for controlling a valve having a valve rod, said actuator comprising: a housing; an actuator spindle arranged at least partly inside said housing, said actuator spindle being arranged to control the movement of a valve rod; a manual override arrangement for manually moving said actuator spindle, said manual override arrangement comprising: a locking element, an actuator spindle holder housing at least a portion of said actuator spindle, and a locking arrangement having a first engaging portion comprised in said locking element and a second engaging portion comprised in said actuator spindle holder, said second engaging portion being arranged to engage with said first engaging portion, a guiding arrangement for guiding the actuator spindle, said guiding arrangement having first guiding means comprised in said actuator spindle holder, and second guiding means comprised in said actuator spindle, such that in a normal operating mode of said actuator, said first engaging portion engages with said second engaging portion whereby said actuator spindle holder is locked to said locking element, and said actuator spindle is guidable along said actuator spindle holder via said guiding arrangement; wherein in a manual override operating mode, said second engaging portion is disengaged from said first engaging portion whereby said actuator spindle holder is unlocked from said locking element, and said actuator spindle holder is rotatable together with said actuator spindle via said guiding arrangement, characterized in that the locking element is arranged internally of the housing of the actuator and is attached to a base portion inside said housing. a housing; an actuator spindle arranged at least partly inside said housing, said actuator spindle being arranged to control the movement of a valve rod; a manual override arrangement for manually moving said actuator spindle, said manual override arrangement comprising: a locking element, an actuator spindle holder housing at least a portion of said actuator spindle, and a locking arrangement having a first engaging portion comprised in said locking element and a second engaging portion comprised in said actuator spindle holder, said second engaging portion being arranged to engage with said first engaging portion, a locking element, an actuator spindle holder housing at least a portion of said actuator spindle, and a locking arrangement having a first engaging portion comprised in said locking element and a second engaging portion comprised in said actuator spindle holder, said second engaging portion being arranged to engage with said first engaging portion, a guiding arrangement for guiding the actuator spindle, said guiding arrangement having first guiding means comprised in said actuator spindle holder, and second guiding means comprised in said actuator spindle, such that in a normal operating mode of said actuator, said first engaging portion engages with said second engaging portion whereby said actuator spindle holder is locked to said locking element, and said actuator spindle is guidable along said actuator spindle holder via said guiding arrangement; wherein in a manual override operating mode, said second engaging portion is disengaged from said first engaging portion whereby said actuator spindle holder is unlocked from said locking element, and said actuator spindle holder is rotatable together with said actuator spindle via said guiding arrangement, characterized in that the locking element is arranged internally of the housing of the actuator and is attached to a base portion inside said housing.