A hair cutting system comprising a cutting head and an attachment which is releasably connectable to the cutting head, the cutting head comprising: - a stationary cutting member comprising a first wall portion and a second wall portion, which are mutually connected by means of a bent intermediate wall portion wherein a plurality of primary cutter teeth having a bent cross-section is provided; and - a movable cutting member which is moveable in a reciprocating manner along a cutter axis in a guiding space enclosed by the first and second wall portions of the stationary cutting member and which comprises a plurality of secondary cutter teeth for co-operation with the primary cutter teeth; wherein the first wall portion and the second wall portion each have an inner surface (120a, 122a) and an outer surface (120b, 122b), wherein the inner surfaces of the first and second wall portions face each other, and wherein the outer surface of the first wall portion is part of a skin facing surface of the cutting head which faces a user's skin during operation; wherein the plurality of primary cutter teeth define a cutting zone of the cutting head extending parallel to the cutter axis and having a length; and wherein the stationary cutting member has opposite first and second sides (112, 114) spaced apart in a direction parallel to the cutter axis; the attachment comprising: - first and second side portions (24, 26) configured to cover, respectively, the first and second sides of the stationary cutting member when the attachment is connected to the cutting head; and - an intermediate portion interconnecting the first and second side portions of the attachment and configured to cover the outer surface of the first wall portion when the attachment is connected to the cutting head; wherein, when the attachment is connected to the cutting head: - the first and second side portions of the attachment protrude relative to the primary cutter teeth in a direction perpendicular to the cutter axis and parallel to the first wall portion; and - the first and second side portions of the attachment and the intermediate portion define a recess exposing the primary cutter teeth, the recess extending in a direction parallel to the cutter axis and being non-interrupted in said direction parallel to the cutter axis over a distance of at least 50% of the length of the cutting zone; characterized in that the first and second side portions (24, 26) of the attachment each have a convex outer surface (54, 56), seen in a cross-section parallel to the first wall portion when the attachment is connected to the cutting head. - a stationary cutting member comprising a first wall portion and a second wall portion, which are mutually connected by means of a bent intermediate wall portion wherein a plurality of primary cutter teeth having a bent cross-section is provided; and - a movable cutting member which is moveable in a reciprocating manner along a cutter axis in a guiding space enclosed by the first and second wall portions of the stationary cutting member and which comprises a plurality of secondary cutter teeth for co-operation with the primary cutter teeth; - first and second side portions (24, 26) configured to cover, respectively, the first and second sides of the stationary cutting member when the attachment is connected to the cutting head; and - an intermediate portion interconnecting the first and second side portions of the attachment and configured to cover the outer surface of the first wall portion when the attachment is connected to the cutting head; - the first and second side portions of the attachment protrude relative to the primary cutter teeth in a direction perpendicular to the cutter axis and parallel to the first wall portion; and - the first and second side portions of the attachment and the intermediate portion define a recess exposing the primary cutter teeth, the recess extending in a direction parallel to the cutter axis and being non-interrupted in said direction parallel to the cutter axis over a distance of at least 50% of the length of the cutting zone;