diff --git a/phpseclib/File/X509.php b/phpseclib/File/X509.php
index d6627187..13ba2bdd 100644
--- a/phpseclib/File/X509.php
+++ b/phpseclib/File/X509.php
@@ -42,6 +42,8 @@
  * @link      http://phpseclib.sourceforge.net
  */
 
+use \phpseclib\Math\BigInteger;
+
 /**
  * Include File_ASN1
  */