An immersion lithographic apparatus includes a projection system. The projection system is configured to project a patterned radiation beam through an immersion liquid onto a target portion of a substrate. An external surface of the projection system includes a first surface. The first surface has a non-planar shape. An element is attached to the first surface and positioned so that at least a portion of the element contacts the immersion liquid in use. The element includes a closed loop of continuously integral material in a preformed state and conforms to the non-planar shape of the first surface.