An adaptor (130, 230, 330, 430, 530, 630) for a drug delivery device having a reservoir and a longitudinal tip, the tip having an outer surface and a longitudinal channel for dispensing any material stored into the reservoir, the adaptor (130, 230, 330, 430, 530, 630) comprising a distal part (130a, 230a, 330a, 430a, 530a, 630a) defining a connecting ring intended to receive a connector, and a proximal part (130b, 230b, 330b, 430b, 530b, 630b) defining a mounting ring (133, 233, 433, 533, 633) having an inner surface (134, 234, 334, 434, 534, 634), the mounting ring (133, 233, 433, 533, 633) being shaped and configured such that, when the adaptor (130, 230, 330, 430, 530, 630) is mounted around the longitudinal tip of the drug delivery device, at least one annular space is created between said inner surface (134, 234, 334, 434, 534, 634) of the mounting ring (133, 233, 433, 533, 633) and said outer surface of the longitudinal tip, said at least one annular space being able to accommodate an adhesive layer in order to bond said adaptor (130, 230, 330, 430, 530, 630) to said longitudinal tip, characterized in that an annular ring (136, 236, 336, 436, 536, 636) is provided at the distal extremity of the inner surface (134, 234, 334, 434, 534, 634) of the mounting ring, wherein the inner surface (134, 234, 334, 434, 534, 634) of the mounting ring (133,, 233, 433, 533, 633) comprises at least one protrusion (135, 235, 335, 435, 535, 635) such that, when the adaptor (130, 230, 330, 430, 530) is mounted around the longitudinal tip of the drug delivery device, said at least one protrusion (135, 235, 335, 435, 535, 635) protrudes into said at least one annular space, said protrusions being in the form of longitudinal ribs, wherein the longitudinal ribs (135, 235) extend on the whole length of the mounting ring (133, 233). the tip having an outer surface and a longitudinal channel for dispensing any material stored into the reservoir, the adaptor (130, 230, 330, 430, 530, 630) comprising a distal part (130a, 230a, 330a, 430a, 530a, 630a) defining a connecting ring intended to receive a connector, and a proximal part (130b, 230b, 330b, 430b, 530b, 630b) defining a mounting ring (133, 233, 433, 533, 633) having an inner surface (134, 234, 334, 434, 534, 634), the mounting ring (133, 233, 433, 533, 633) being shaped and configured such that, when the adaptor (130, 230, 330, 430, 530, 630) is mounted around the longitudinal tip of the drug delivery device, at least one annular space is created between said inner surface (134, 234, 334, 434, 534, 634) of the mounting ring (133, 233, 433, 533, 633) and said outer surface of the longitudinal tip, said at least one annular space being able to accommodate an adhesive layer in order to bond said adaptor (130, 230, 330, 430, 530, 630) to said longitudinal tip, characterized in that an annular ring (136, 236, 336, 436, 536, 636) is provided at the distal extremity of the inner surface (134, 234, 334, 434, 534, 634) of the mounting ring, wherein the inner surface (134, 234, 334, 434, 534, 634) of the mounting ring (133,, 233, 433, 533, 633) comprises at least one protrusion (135, 235, 335, 435, 535, 635) such that, when the adaptor (130, 230, 330, 430, 530) is mounted around the longitudinal tip of the drug delivery device, said at least one protrusion (135, 235, 335, 435, 535, 635) protrudes into said at least one annular space, said protrusions being in the form of longitudinal ribs, wherein the longitudinal ribs (135, 235) extend on the whole length of the mounting ring (133, 233).