diff --git a/src/cairo-clip-boxes.c b/src/cairo-clip-boxes.c
index bbb4197..4cdc3e5 100644
--- a/src/cairo-clip-boxes.c
+++ b/src/cairo-clip-boxes.c
@@ -159,6 +159,8 @@ _cairo_clip_intersect_rectangle_box (cairo_clip_t *clip,
     cairo_bool_t changed = FALSE;
     int i, j;
 
+    assert (! _cairo_clip_is_all_clipped (clip));
+
     if (clip == NULL) {
 	clip = _cairo_clip_create ();
 	if (clip == NULL)
@@ -258,6 +260,9 @@ _cairo_clip_intersect_box (cairo_clip_t *clip,
 {
     cairo_rectangle_int_t r;
 
+    if (_cairo_clip_is_all_clipped (clip))
+	return clip;
+
     _cairo_box_round_to_rectangle (box, &r);
     if (r.width == 0 || r.height == 0)
 	return _cairo_clip_set_all_clipped (clip);