diff --git a/install.php b/install.php
index a59b9469de..c49043e5c6 100644
--- a/install.php
+++ b/install.php
@@ -230,7 +230,7 @@ function checkPrereqs()
     }
 
     $reqs = array('gd', 'curl',
-                  'xmlwriter', 'mbstring');
+                  'xmlwriter', 'mbstring','tidy');
 
     foreach ($reqs as $req) {
         if (!checkExtension($req)) {