The invention relates to an interlock mechanism for defining an operation sequence of an auto-injector (1) in a manner to allow a lateral trigger button (16) to be operated only when a proximal end (P) of the auto-injector (1) is pressed against an injection site, wherein a detector means (18) is arranged inside an elongate housing (2) of the auto-injector (1) at the proximal end (P), the detector means (18) slidable in longitudinal direction and biased by a detector spring (19) into a position with the detector means (18) protruding beyond the proximal end (P), wherein a dog (16.2) is arranged at the trigger button (16) and wherein at least one longitudinal bar (18.1, 21) is provided, at least one of the bars (21) slidable in longitudinal direction and coupled to the detector means (18) for joint movement at least in distal direction (D), wherein a recess (21.1) for the dog (16.2) is provided in the bar (21) for allowing the trigger button (16) to be pressed when the detector means (18) is being pushed into the auto-injector (1) and wherein otherwise the dog (16.2) is engaged with the bar (21) in a manner to prevent the trigger button (16) from being pressed.
