An aerosol-generating device is provided, including: a device housing defining a cavity; an adjustable retaining element positioned in or adjacent to the cavity and defining a passage; and an actuation means configured to actuate the adjustable retaining element between a receiving position and a retaining position, a cross-sectional dimension of the passage being greater when the adjustable retaining element is in the receiving position than when the adjustable retaining element is in the retaining position, and the adjustable retaining element further defining a passage entrance and a passage exit and including a surface defined between the passage entrance and the passage exit, a longitudinal cross-section of the surface having a curved shape when the adjustable retaining element is in the retaining position, a portion of the curved shape comprising a convex curve defining a constriction in the passage at a turning point of the convex curve.