It is well established that there is a strong boundary wave during low‐frequency grazing scatter at a rough rigid surface overlaid by a homogeneous medium. Tolstoy [J. Acoust. Soc. Am.69, 1290–1298 (1981)] has also shown that when source and receiver are on the bottom and the velocity in the medium decreases away from the ocean bottom the boundary wave tunnels into the shadow zone. We consider the case when source and receiver are near the ocean surface. It is predicted that, under certain conditions of velocity gradient, frequency and bottom roughness, the addition of the boundary wave mode to the volume wave mode will change the path of the grazing specularly scattered ray above the rough bottom. As a result, an upward refracted ray will reach the surface at a skip distance significantly greater than for a smooth bottom. This modified refraction phenomenon should be detectable at sea, under suitable indicated experimental conditions.