Heat exchanger for an internal combustion engine, for the transfer of heat between at least two fluids (12, 14), - with at least one housing which has at least one housing wall and a housing interior space which is delimited at least in regions by means of the housing wall and has a fluid inlet region for introducing a first fluid of the at least two fluids (12, 14) into the housing interior space and a fluid outlet region for discharging the first fluid from the housing interior space, and - with at least one fluid duct apparatus which is arranged in an interior space part region of the housing interior space and has a fluid duct apparatus wall which is configured to separate the first fluid from a second fluid and, at least in regions, delimits a plurality of fluid ducts (50, 52, 54, 56, 58, 60, 62, 64, 66, 68) of the fluid duct apparatus for conducting the first fluid between the fluid inlet region and the fluid outlet region, at least one of the fluid ducts (50, 52, 54, 56, 58, 60, 62, 64, 66, 68) having an undulating course at least in regions in the longitudinal extent direction (x) of the fluid duct apparatus, wherein the fluid duct apparatus comprises at least one supporting element which is arranged between a first fluid duct wall, which has the undulating course at least in regions and delimits a first outer fluid duct of the plurality of fluid ducts (50, 52, 54, 56, 58, 60, 62, 64, 66, 68) at least in regions, and the fluid duct apparatus wall, and has a first supporting element region which is supported against the first fluid duct wall, wherein the at least one supporting element is provided to seal the first outer fluid duct with respect to a passage of the first fluid, characterized in that the supporting element has a first supporting element region, which is of complementary shape at least in regions with respect to the undulating course. - with at least one housing which has at least one housing wall and a housing interior space which is delimited at least in regions by means of the housing wall and has a fluid inlet region for introducing a first fluid of the at least two fluids (12, 14) into the housing interior space and a fluid outlet region for discharging the first fluid from the housing interior space, and - with at least one fluid duct apparatus which is arranged in an interior space part region of the housing interior space and has a fluid duct apparatus wall which is configured to separate the first fluid from a second fluid and, at least in regions, delimits a plurality of fluid ducts (50, 52, 54, 56, 58, 60, 62, 64, 66, 68) of the fluid duct apparatus for conducting the first fluid between the fluid inlet region and the fluid outlet region, at least one of the fluid ducts (50, 52, 54, 56, 58, 60, 62, 64, 66, 68) having an undulating course at least in regions in the longitudinal extent direction (x) of the fluid duct apparatus, the fluid duct apparatus comprises at least one supporting element which is arranged between a first fluid duct wall, which has the undulating course at least in regions and delimits a first outer fluid duct of the plurality of fluid ducts (50, 52, 54, 56, 58, 60, 62, 64, 66, 68) at least in regions, and the fluid duct apparatus wall, and has a first supporting element region which is supported against the first fluid duct wall, wherein the at least one supporting element is provided to seal the first outer fluid duct with respect to a passage of the first fluid, characterized in that the supporting element has a first supporting element region, which is of complementary shape at least in regions with respect to the undulating course.