This adaptor (1) comprises a tubular body (2) having a proximal region (4) and a distal region (6), the proximal region (4) being provided with engaging means for mounting the adaptor (1) on a distal tip of said drug delivery device and the distal region (6) being provided with connecting means for connecting the adaptor (1) to the connector. The distal region (6) has a distal end (15) delimiting a distal opening (16) so as to permit introduction of the connector inside the distal region (6). The distal end (15) comprises clamping means so as to clamp the connector as soon as said connector is introduced inside the tubular body (2). The clamping means comprise a deformable element (17) having a free end (18) which is configured to deform towards the proximal region (4) when the connector is introduced inside the tubular body (2).
