diff --git a/scene.cpp b/scene.cpp
index 5c48cdc40e..9a9d3deabd 100644
--- a/scene.cpp
+++ b/scene.cpp
@@ -355,6 +355,8 @@ QRegion Scene::Window::shape() const
                     shape_region += QRegion( rects[ i ].x, rects[ i ].y,
                         rects[ i ].width, rects[ i ].height );
                 XFree(rects);
+                // make sure the shape is sane (X is async, maybe even XShape is broken)
+                shape_region &= QRegion( 0, 0, width(), height());
                 }
             else
                 shape_region = QRegion();