A film cassette comprises a film spool supported inside a lighttight cassette shell for rotation to thrust a filmstrip coiled about the spool automatically to the exterior of the shell, and a film exposure status indicator supported for movement with respect to the shell from an unexposed position for providing a visible indication that the filmstrip is unexposed to an exposed position for providing a visible indication that the filmstrip is exposed. According to the invention, the shell and the status indicator include mutually engagable pin and hole for locking the indicator in its unexposed position to prevent the indicator from being manually moved to its exposed position but which can be disengaged by a suitable device in a camera, for example, to unlock the indicator to permit the indicator to be mechanically moved to the exposed position.