The invention relates to an automatic-lung regulator for compressed-air respiration apparatus, comprising a diaphragm (2) that can be actuated by respiration for controlling the air supply. Said regulator has a fixing moulded body (5) on a locking lever (1) for locking the diaphragm in an operating phase, said body being maintained in a release or locking position by a first spring element (4). A second spring element (10), which can be displaced in a longitudinal direction in a limited manner, acts as a safety fixing element in order to reinforce the locking action of the locking lever, when the automatic-lung regulator is subjected to external mechanical influences.