diff --git a/wp-includes/formatting.php b/wp-includes/formatting.php
index cb8b372e97..b20c2d3a49 100644
--- a/wp-includes/formatting.php
+++ b/wp-includes/formatting.php
@@ -636,11 +636,17 @@ function wp_rel_nofollow( $text ) {
 	global $wpdb;
 	// This is a pre save filter, so text is already escaped.
 	$text = stripslashes($text);
-	$text = preg_replace('|<a (.+?)>|ie', "'<a ' . str_replace(' rel=\"nofollow\"','',stripslashes('$1')) . ' rel=\"nofollow\">'", $text);
+	$text = preg_replace_callback('|<a (.+?)>|i', 'wp_rel_nofollow_callback', $text);
 	$text = $wpdb->escape($text);
 	return $text;
 }
 
+function wp_rel_nofollow_callback( $matches ) {
+	$text = $matches[1];
+	$text = str_replace(array(' rel="nofollow"', " rel='nofollow'"), '', $text);
+	return "<a $text rel=\"nofollow\">";
+}
+
 function convert_smilies($text) {
 	global $wp_smiliessearch, $wp_smiliesreplace;
     $output = '';