a heat - exchanger includes a plurality of stacked tubular elements each having tanks , and passage - forming protrusions defining a passage connecting the tanks , fins interposed between adjacent ones of the tubular elements and contacting the passage - forming protrusions , inlet / outlet units each comprising a barrel - shaped element protruding from and open to the tank of a respective one of the tubular elements , inlet / outlet pipes fitted coaxially in contact with and joined to the barrel - shaped elements , respectively , and a measure for preventing parts of the barrel - shaped elements from being deformed as the inlet / outlet pipes are fitted to the barrel - shaped elements during the assembly of the heat exchanger to in turn maintain the integrity of the joints between the inlet / outlet units and the inlet / outlet pipes . the reinforcement may include a ring disposed around the barrel - shaped element adjacent an end thereof . when the inlet / outlet pipe is fitted into and in contact with the barrel - shaped element , the ring prevents the parts of the barrel - shaped element from being forced outwardly . the reinforcement may also include , in an addition or as an alternative to the ring , at least one protrusion extending from the parts of the barrel - shaped element and contacting the inlet / outlet pipe fitted to the barrel - shaped element . the at least one protrusion prevents the inlet / outlet pipe from being moved too far axially relative to the barrel - shaped element thereby ensuring that the inlet / outlet pipe does not deform the parts of the barrel - shaped element .