diff --git a/src/Mailto.php b/src/Mailto.php
index 334548d..d33b1ad 100644
--- a/src/Mailto.php
+++ b/src/Mailto.php
@@ -1,5 +1,5 @@
 <?php namespace Locker\XApi;
 
 class Mailto extends RegexpAtom {
-  protected static $pattern = '/^mailto:[A-Z0-9.\'_%+-]+@[A-Z0-9.-]+\.[A-Z]{1,63}$/i';
+  protected static $pattern = '/^mailto:[A-Z0-9.`\'_%+-]+@[A-Z0-9.-]+\.[A-Z]{1,63}$/i';
 }