diff --git a/selectors-4/Overview.bs b/selectors-4/Overview.bs
index c7bc18dcf5d3..ca084270950f 100644
--- a/selectors-4/Overview.bs
+++ b/selectors-4/Overview.bs
@@ -1219,6 +1219,7 @@ The Relational Pseudo-class: '':has()''</h3>
 		which contains anything that's not a heading element.
 	</div>
 
+	'':has()'' pseudo-class cannot be nested; '':has()'' is not valid within '':has()''.
 
 <h2 id="elemental-selectors">
 Elemental selectors</h2>