Heat exchanger for an internal combustion engine, for the transfer of heat between at least two fluids , - 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 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 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 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 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 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 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 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 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 . <EOS>