diff --git a/libweston/input.c b/libweston/input.c
index f2a9a07a..338be6c3 100644
--- a/libweston/input.c
+++ b/libweston/input.c
@@ -4786,6 +4786,7 @@ maybe_warp_confined_pointer(struct weston_pointer_constraint *constraint)
 		pixman_region32_intersect(&confine_region,
 					  &constraint->view->surface->input,
 					  &constraint->region);
+		assert(!pixman_region32_selfcheck(&confine_region));
 		region_to_outline(&confine_region, &borders);
 		pixman_region32_fini(&confine_region);