Heat exchanger comprising: a coolant housing having a border which defines an opening; and a header plate arranged to cover the opening; wherein the header plate crimps the border of the coolant housing by encompassing a free edge portion, an outer side surface portion and an outer upper surface portion on at least two opposing locations on the border; whereby a closed cavity for coolant is defined by the coolant housing and the header plate; and wherein the header plate is provided with apertures, each aperture receiving a tube for guiding coolant from or to the closed cavity; the heat exchanger further comprising: a reinforcing plate extending between two opposing locations on the border of the coolant housing, and extending on the outside of the header plate in view of the closed cavity, the reinforcing plate being made of the same material as the header plate and the tubes; wherein the reinforcing plate is joined, at each of said opposing locations, to an outer surface portion of the header plate encompassing a corner C2 between the free edge portion of the coolant housing and the outer side surface portion of the border; wherein the reinforcing plate is provided with at least one aperture embracing more than one of the tubes which are received by the header plate; and wherein the reinforcing plate is arranged to provide a gap between the reinforcing plate and the more than one tubes embraced by the apertures of the reinforcing plate. a coolant housing having a border which defines an opening; and a header plate arranged to cover the opening; wherein the header plate crimps the border of the coolant housing by encompassing a free edge portion, an outer side surface portion and an outer upper surface portion on at least two opposing locations on the border; whereby a closed cavity for coolant is defined by the coolant housing and the header plate; and wherein the header plate is provided with apertures, each aperture receiving a tube for guiding coolant from or to the closed cavity; the heat exchanger further comprising: a reinforcing plate extending between two opposing locations on the border of the coolant housing, and extending on the outside of the header plate in view of the closed cavity, the reinforcing plate being made of the same material as the header plate and the tubes; wherein the reinforcing plate is joined, at each of said opposing locations, to an outer surface portion of the header plate encompassing a corner C2 between the free edge portion of the coolant housing and the outer side surface portion of the border; wherein the reinforcing plate is provided with at least one aperture embracing more than one of the tubes which are received by the header plate; and wherein the reinforcing plate is arranged to provide a gap between the reinforcing plate and the more than one tubes embraced by the apertures of the reinforcing plate. a reinforcing plate extending between two opposing locations on the border of the coolant housing, and extending on the outside of the header plate in view of the closed cavity, the reinforcing plate being made of the same material as the header plate and the tubes; wherein the reinforcing plate is joined, at each of said opposing locations, to an outer surface portion of the header plate encompassing a corner C2 between the free edge portion of the coolant housing and the outer side surface portion of the border; wherein the reinforcing plate is provided with at least one aperture embracing more than one of the tubes which are received by the header plate; and wherein the reinforcing plate is arranged to provide a gap between the reinforcing plate and the more than one tubes embraced by the apertures of the reinforcing plate.