An assembly for a drug delivery device (1), comprising: - a housing (2) having a proximal limb and a distal limb, - a piston rod 5 (8) that is adapted to be displaced distally with respect to the housing (2) away from a proximal starting position and towards a distal end position to administer a drug (31), - an indicator (13) to indicate at least two different operating states of the assembly, the indicator being mobile (13) with respect to the housing (2) from a first indication position for a first state of the assembly to a second indication position for a second state of the assembly, wherein - the piston rod (8) and the indicator (13 ) are configured to interact mechanically to convert the movement of the piston rod (8) into movement of the indicator (13) and characterized by - a first latch (21) provided in the indicator (13), which is configured to ensure that the indicator (13) can be released in the first indication position such that movement to the second indication position is allowed, and by - a second latch (22) provided in the indicator (13 ), which is configured to secure the indicator (13) in the second indication position such that movement to the first indication position is prevented.Un conjunto para un dispositivo (1) de administración de fármacos, que comprende: - un alojamiento (2) que tiene una extremidad proximal y una extremidad distal, - un vástago 5 de pistón (8) que está adaptado para ser desplazado de manera distal con respecto al alojamiento (2) lejos de una posición de inicio proximal y hacia una posición final distal para administrar un fármaco (31), - un indicador (13) para indicar al menos dos estados de operación diferentes del conjunto, siendo móvil el indicador (13) con respecto al alojamiento (2) desde una primera posición de indicación para un primer estado del conjunto a una segunda posición de indicación para un segundo estado del conjunto, en donde - el vástago de pistón (8) y el indicador (13) están configurados para inter
