Headrest system for a motor vehicle seat, said system comprising: - a headrest provided with a frame, said frame comprising a first and a second parallel rod, the upper ends of which are connected to each other by a crosspiece, the upper part of said frame being covered by a pad, at least said first rod being provided with an anti-extraction notch in the form of a trench, said notch having: -- a lower locking face for blocking said first rod from sliding upwards, -- an upper face for blocking said first rod from sliding downwards, said first rod being provided with a main chamfer opening onto said upper face, - a first and a second sleeve for slidingly receiving said first and second rod respectively, said sleeves being intended to be mounted at the top of the back of said seat, at least said first sleeve being provided: -- with a radially slidable spool having a locking edge arranged to be able to be inserted into said notch when they are facing each other, -- with a spring for actuating said spool towards said first rod so as to allow the gradual insertion of said edge into said notch when said first rod is slid upwards, said edge sliding against said main chamfer until it is inserted into said notch, said system being characterised in that said main chamfer is provided at each of its ends with a respective secondary chamfer (13a, 13b) such that said edge can slide against one of said secondary chamfers until it is inserted into said notch in the event of rotational movement of said first rod on either side of its nominal position along the axis of extension of said first rod. - a headrest provided with a frame, said frame comprising a first and a second parallel rod, the upper ends of which are connected to each other by a crosspiece, the upper part of said frame being covered by a pad, at least said first rod being provided with an anti-extraction notch in the form of a trench, said notch having: -- a lower locking face for blocking said first rod from sliding upwards, -- an upper face for blocking said first rod from sliding downwards, said first rod being provided with a main chamfer opening onto said upper face, -- a lower locking face for blocking said first rod from sliding upwards, -- an upper face for blocking said first rod from sliding downwards, said first rod being provided with a main chamfer opening onto said upper face, - a first and a second sleeve for slidingly receiving said first and second rod respectively, said sleeves being intended to be mounted at the top of the back of said seat, at least said first sleeve being provided: -- with a radially slidable spool having a locking edge arranged to be able to be inserted into said notch when they are facing each other, -- with a spring for actuating said spool towards said first rod so as to allow the gradual insertion of said edge into said notch when said first rod is slid upwards, said edge sliding against said main chamfer until it is inserted into said notch, -- with a radially slidable spool having a locking edge arranged to be able to be inserted into said notch when they are facing each other, -- with a spring for actuating said spool towards said first rod so as to allow the gradual insertion of said edge into said notch when said first rod is slid upwards, said edge sliding against said main chamfer until it is inserted into said notch,