diff --git a/lib/kses.php b/lib/kses.php
index 578aadfcd05..476f2c380ce 100644
--- a/lib/kses.php
+++ b/lib/kses.php
@@ -471,7 +471,7 @@ function kses_bad_protocol_once($string, $allowed_protocols)
 {
   return preg_replace('/^((&[^;]*;|[\sA-Za-z0-9])*)'.
                       '(:|&#0*58;|&#[Xx]0*3[Aa];)\s*/e',
-                      'kses_bad_protocol_once2("\\1", $allowed_protocols)',
+                      'kses_bad_protocol_once2(\'\\1\', $allowed_protocols)',
                       $string);
 } # function kses_bad_protocol_once