An elongate heat exchanger for cooling hot gas includes an arrangement for reducing thermal stresses when mounted in a housing. A pair of planar extensions project from opposite sides of the core. A mounting bracket has a central portion adapted to extend across the top of the core, and a pair of edge portions projecting outwardly from the central portion. The edge portions are substantially parallel to the planar extensions, and each has a top layer at least partially covering one of the planar extensions, wherein each of the edge portions is adapted to be secured to the housing, for example by a bolt. Each planar extension may be slidably received in a slot between the top and bottom layers of the edge portion, or may be slidably received between the top layer and the housing, to permit longitudinal thermal expansion of the core.