A shaving unit comprising a housing (10, 110) and at least one cutting unit (3 a, 3b) accommodated and supported by the housing, wherein each cutting unit comprises: - an external cutting member having a plurality of hair-entry openings; and - an internal cutting member which is rotatable relative to the external cutting member about an axis of rotation (5a, 5b); wherein the shaving unit comprises, for each cutting unit, a locking system configured and arranged to prevent, during use, rotation of the external cutting member of the respective cutting unit relative to the housing at least in a rotational direction of the internal cutting member about the axis of rotation, said locking system comprising a first locking member (150a, 150b, 150c) connected to one of the housing and the external cutting member and a second locking member connected to the other one of the housing and the external cutting member for cooperation with the first locking member, characterized in that the first locking member comprises an annular array of N1 first arresting elements (150a, 150b, 150c) which are concentrically arranged relative to the axis of rotation (5a, 5b) with a uniform distribution about the axis of rotation, and in that the second locking member comprises N2 second arresting elements (161a, 161b), wherein: N 1 ≥ 8 and 1 ≤ N2 ≤ N1; - the N2 second arresting elements are configured and arranged to be each engageable with a respective one of the N1 first arresting elements in any of N1 angular positions of the external cutting member about the axis of rotation relative to the housing (10, 110); and - each of the N2 second arresting elements is configured and arranged to prevent rotation of the external cutting member relative to the housing in said rotational direction by engagement with said respective one of the N1 first arresting elements in any of said N1 angular positions of the external cutting member. - an external cutting member having a plurality of hair-entry openings; and - an internal cutting member which is rotatable relative to the external cutting member about an axis of rotation (5a, 5b); wherein the shaving unit comprises, for each cutting unit, a locking system configured and arranged to prevent, during use, rotation of the external cutting member of the respective cutting unit relative to the housing at least in a rotational direction of the internal cutting member about the axis of rotation, said locking system comprising a first locking member (150a, 150b, 150c) connected to one of the housing and the external cutting member and a second locking member connected to the other one of the housing and the external cutting member for cooperation with the first locking member, characterized in that the first locking member comprises an annular array of N1 first arresting elements (150a, 150b, 150c) which are concentrically arranged relative to the axis of rotation (5a, 5b) with a uniform distribution about the axis of rotation, and in that the second locking member comprises N2 second arresting elements (161a, 161b), wherein: N 1 ≥ 8 and 1 ≤ N2 ≤ N1; wherein the shaving unit comprises, for each cutting unit, a locking system configured and arranged to prevent, during use, rotation of the external cutting member of the respective cutting unit relative to the housing at least in a rotational direction of the internal cutting member about the axis of rotation, said locking system comprising a first locking member (150a, 150b, 150c) connected to one of the housing and the external cutting member and a second locking member connected to the other one of the housing and the external cutting member for cooperation with the first locking member, characterized in that the first locking member comprises an annular array of N1 first arresting elements (150a, 150b, 150c) which are concentrically arranged relative to the axis of rotation (5a, 5b) with a uniform distribution about the axis of rotation, and in that the second locking member comprises N2 second arresting elements (161a, 161b), wherein: N 1 ≥ 8 and 1 ≤ N2 ≤ N1; - the N2 second arresting elements are configured and arranged to be each engageable with a respective one of the N1 first arresting elements in any of N1 angular positions of the external cutting member about the axis of rotation relative to the housing (10, 110); and - each of the N2 second arresting elements is configured and arranged to prevent rotation of the external cutting member relative to the housing in said rotational direction by engagement with said respective one of the N1 first arresting elements in any of said N1 angular positions of the external cutting member.