diff --git a/src/applications/system/controller/PhabricatorRobotsController.php b/src/applications/system/controller/PhabricatorRobotsController.php
--- a/src/applications/system/controller/PhabricatorRobotsController.php
+++ b/src/applications/system/controller/PhabricatorRobotsController.php
@@ -20,6 +20,7 @@
 
     $out[] = 'User-Agent: *';
     $out[] = 'Disallow: /diffusion/';
+    $out[] = 'Disallow: /source/';
 
     // Add a small crawl delay (number of seconds between requests) for spiders
     // which respect it. The intent here is to prevent spiders from affecting