diff --git a/wp-includes/ms-default-filters.php b/wp-includes/ms-default-filters.php
index 3ba2ea9fb..cabace17f 100644
--- a/wp-includes/ms-default-filters.php
+++ b/wp-includes/ms-default-filters.php
@@ -35,7 +35,7 @@ add_filter ( 'upload_mimes', 'check_upload_mimes' );
 add_filter ( 'wp_mail_from', 'wordpressmu_wp_mail_from' );
 
 
-add_action( "phpmailer_init", "fix_phpmailer_messageid" );
+add_action( 'phpmailer_init', 'fix_phpmailer_messageid' );
 
 // Disable somethings by default for multisite
 add_filter( 'enable_update_services_configuration', '__return_false' );