diff --git a/includes/class-wp-push-syndication-server.php b/includes/class-wp-push-syndication-server.php
index 5884e70fa3532a9ade130979709039ef8fcde001..e0f46a7bf1b69baa57f9ace733e6a4d71b525de0 100644
--- a/includes/class-wp-push-syndication-server.php
+++ b/includes/class-wp-push-syndication-server.php
@@ -1051,7 +1051,7 @@ class WP_Push_Syndication_Server {
 		return $result;
 	}
 
-	private update_slave_post_states( $post_id, $slave_post_states ) {
+	private function update_slave_post_states( $post_id, $slave_post_states ) {
 		update_post_meta( $post_id, '_syn_slave_post_states', $slave_post_states );
 	}