diff --git a/src/compton.c b/src/compton.c
index 4af886c..e9dff9a 100644
--- a/src/compton.c
+++ b/src/compton.c
@@ -511,6 +511,9 @@ static struct managed_win *paint_preprocess(session_t *ps, bool *fade_running) {
 		    w->g.y + w->g.height < 1 || w->g.x >= ps->root_width ||
 		    w->g.y >= ps->root_height || w->state == WSTATE_UNMAPPED ||
 		    (double)w->opacity * MAX_ALPHA < 1 || w->paint_excluded) {
+			// TODO: for consistency, even a window has 0 opacity, we still
+			// probably need to blur its background, so to_paint shouldn't be
+			// false for them.
 			to_paint = false;
 		}