The present invention relates to adaptor (30) for a drug delivery device having a reservoir (12) and a longitudinal tip (20), the adaptor (30) comprising a distal part defining a connecting ring (31) intended to receive a connector, and a proximal part defining a mounting ring (33) having an inner surface (34), the mounting ring (33) being shaped and configured such that, when the adaptor (30) is mounted around the longitudinal tip (20) of the drug delivery device, at least one annular space (38) is created between said inner surface (34) of the mounting ring (33) and said outer surface (20a) of the longitudinal tip (20), said at least one annular space (38) being able to accommodate an adhesive layer (40) in order to bond said adaptor (30) to said longitudinal tip. The invention further relates to a drug delivery device comprising such an adaptor.