A heat exchanger, in particular an intercooler, is provided that includes at least one collector box that has a base. At least one tube engages into a passage in an approximately perpendicular manner with respect to the base, the passage protruding out of the base and surrounding a tube end, and the passage has a rectangular cross-section that is adapted to the outer circumference of the tube. The aim of the invention is to further extend the service life of the heat exchanger with a further reduction of the wall thickness of the collector box base as well as of the tube. This is achieved in that a wall thickness of the passage is thinned at least in a corner region.