diff --git a/library/HTMLPurifier/AttrDef/URI/Host.php b/library/HTMLPurifier/AttrDef/URI/Host.php
index 1beeaa5d..ddc5dfbe 100644
--- a/library/HTMLPurifier/AttrDef/URI/Host.php
+++ b/library/HTMLPurifier/AttrDef/URI/Host.php
@@ -106,7 +106,7 @@ class HTMLPurifier_AttrDef_URI_Host extends HTMLPurifier_AttrDef
         // If we have Net_IDNA2 support, we can support IRIs by
         // punycoding them. (This is the most portable thing to do,
         // since otherwise we have to assume browsers support
-        } elseif ($config->get('Core.EnableIDNA')) {
+        } elseif ($config->get('Core.EnableIDNA') && class_exists('Net_IDNA2')) {
             $idna = new Net_IDNA2(array('encoding' => 'utf8', 'overlong' => false, 'strict' => true));
             // we need to encode each period separately
             $parts = explode('.', $string);