diff --git a/wp-includes/formatting.php b/wp-includes/formatting.php
index a1c3f826c5..201f7c8212 100644
--- a/wp-includes/formatting.php
+++ b/wp-includes/formatting.php
@@ -3235,7 +3235,7 @@ function sanitize_mime_type( $mime_type ) {
  * @return string URLs starting with the http or https protocol, separated by a carriage return.
  */
 function sanitize_trackback_urls( $to_ping ) {
-	$urls_to_ping = preg_split( '/\r\n\t /', trim( $to_ping ), -1, PREG_SPLIT_NO_EMPTY );
+	$urls_to_ping = preg_split( '/[\r\n\t ]/', trim( $to_ping ), -1, PREG_SPLIT_NO_EMPTY );
 	foreach ( $urls_to_ping as $k => $url ) {
 		if ( !preg_match( '#^https?://.#i', $url ) )
 			unset( $urls_to_ping[$k] );