diff --git a/verify.php b/verify.php
index 1586814..9b4ef75 100644
--- a/verify.php
+++ b/verify.php
@@ -409,7 +409,8 @@ class verify
     */
   public static function staticIsAllowedChars ($val, $allowedChars)
   {
-    preg_match ('/^['.$allowedChars.']+/u', $val, $matches);
+    $allowedChars = preg_quote ($allowedChars, "#");
+    preg_match ('#^['.$allowedChars.']+#u', $val, $matches);
     if (isset ($matches[0]) &&
         mb_strlen ($matches[0]) === mb_strlen ($val))
       return true;