A fixing system for fixing a helmet bowl on a head of a wearer, having a) a head size adjustment ring with a headband for adjustably placing on the head of the wearer, wherein the headband extends along a circumferential path adjustable to the head; b) at least one first connecting element (3; 46) for regulating the head size adjustment ring on the helmet bowl, wherein - said at least one first connecting element (3; 46) can be anchored with a free first end to the helmet bowl, and - a connection is provided for between said at least one first connecting element (3; 46) and the head size adjustment ring at a second end facing away from the first end of said at least one first connecting element (3; 46), so that c) the second end of said at least one first connecting element (3; 46) and the headband of the head size adjustment ring can be adjusted in their relative position to one another as viewed in a longitudinal direction of the headband, characterised in that d) said at least one first connecting element (3; 46) has two connecting element shanks (17, 18; 47, 48), which can be hinged around a swivel axis (19; 49) and can be transformed in this way from an open position to a folded position, wherein said at least one first connecting element (3; 46) is then, i.e. in the state where it is anchored on the helmet bowl, in the folded position, wherein e) the connection between said at least one first connecting element (3; 46) and the head size adjustment ring is variable, wherein f) the second end of said at least one first connecting element (3; 46) is formed in a loop shape and delimits an adjustment ring receptacle space, wherein the headband is guided through the adjustment ring receptacle space. a) a head size adjustment ring with a headband for adjustably placing on the head of the wearer, wherein the headband extends along a circumferential path adjustable to the head; b) at least one first connecting element (3; 46) for regulating the head size adjustment ring on the helmet bowl, wherein - said at least one first connecting element (3; 46) can be anchored with a free first end to the helmet bowl, and - a connection is provided for between said at least one first connecting element (3; 46) and the head size adjustment ring at a second end facing away from the first end of said at least one first connecting element (3; 46), so that - said at least one first connecting element (3; 46) can be anchored with a free first end to the helmet bowl, and - a connection is provided for between said at least one first connecting element (3; 46) and the head size adjustment ring at a second end facing away from the first end of said at least one first connecting element (3; 46), so that c) the second end of said at least one first connecting element (3; 46) and the headband of the head size adjustment ring can be adjusted in their relative position to one another as viewed in a longitudinal direction of the headband, characterised in that d) said at least one first connecting element (3; 46) has two connecting element shanks (17, 18; 47, 48), which can be hinged around a swivel axis (19; 49) and can be transformed in this way from an open position to a folded position, wherein said at least one first connecting element (3; 46) is then, i.e. in the state where it is anchored on the helmet bowl, in the folded position, wherein e) the connection between said at least one first connecting element (3; 46) and the head size adjustment ring is variable, wherein f) the second end of said at least one first connecting element (3; 46) is formed in a loop shape and delimits an adjustment ring receptacle space, wherein the headband is guided through the adjustment ring receptacle space.