diff --git a/wp-includes/class-wp-comment-query.php b/wp-includes/class-wp-comment-query.php
index 2e65276..09e7e14 100644
--- a/wp-includes/class-wp-comment-query.php
+++ b/wp-includes/class-wp-comment-query.php
@@ -1012,7 +1012,8 @@ class WP_Comment_Query {
 
 		// Prime comment caches for non-top-level comments.
 		$descendant_ids = array();
-		for ( $i = 1; $i < count( $levels ); $i++ ) {
+		$level_count = count( $levels );
+		for ( $i = 1; $i <= $level_count; $i++ ) {
 			$descendant_ids = array_merge( $descendant_ids, $levels[ $i ] );
 		}