diff --git a/src/wp-includes/post.php b/src/wp-includes/post.php
index b225d35c48b2a..242f80cf039ad 100644
--- a/src/wp-includes/post.php
+++ b/src/wp-includes/post.php
@@ -2891,6 +2891,10 @@ function get_post_custom_values( $key = '', $post_id = 0 ) {
 
 	$custom = get_post_custom( $post_id );
 
+	if ( ! is_array( $custom ) ) {
+		return null;
+	}
+
 	return $custom[ $key ] ?? null;
 }