A mechanical decoupler (15) at the inlet to a turbomachine is positioned on the outside of an intake casing, where radiating arms (27) meet an external casing (13) so as to partially unload a low-pressure shaft when a significant out-of-balance appears. Because it is positioned a long way from the bearing, the decoupler (15) can be designed with a greater degree of freedom at a location where there is more space available and where layout constraints are less of an issue. More specifically, it is housed in a cavity (30) of the external casing (13) which opens onto the flow path (5).