the present invention relates to a closing device for sachets comprising at least two complementary closing elements and an associated slider comprising a central bead , adapted for modifying the joining state of said two elements so as to respectively separate or engage the latter according to its direction of motion , characterized in that the slider comprises at least one flexible lip placed on the apex of the central bead opposite a lead angle provided on the closing element , according to a configuration such that any attempt to pull back the slider results in autolocking hanging of the lip .