diff --git a/class-simple-page-ordering.php b/class-simple-page-ordering.php
index db816a5..8098e2d 100644
--- a/class-simple-page-ordering.php
+++ b/class-simple-page-ordering.php
@@ -437,7 +437,7 @@ public static function page_row_actions( $actions, $post ) {
 			if ( 0 === $post->post_parent ) {
 				$siblings = $top_level_pages;
 			} else {
-				$siblings = $children_pages[ $post->post_parent ];
+				$siblings = $children_pages[ $post->post_parent ] ?? [];
 			}
 
 			// Assume no sibling.