An axial flow rotary valve (1) for an internal combustion engine comprising a cylinder head (10) having a bore in which an axial flow rotary valve (1) rotates. The valve having a cylindrical centre portion (4), and an inlet and an exhaust port (2, 3) terminating as openings (7, 8) in the centre portion, the openings periodically communicating with a combustion chamber (23) through a window (15) in the bore. The clearance between the centre portion and the bore being sealed by an array of floating seals comprising at least two axial seals (16a, 16b) spaced apart on opposite sides of the window. The assembly further comprising at least one floating axially extending masking seal (5) being disposed outside the window and circumferentially remote from the axial seals.