diff --git a/modules/comment/controllers/admin_manage_comments.php b/modules/comment/controllers/admin_manage_comments.php
index 0889dc4e..49bd85d5 100644
--- a/modules/comment/controllers/admin_manage_comments.php
+++ b/modules/comment/controllers/admin_manage_comments.php
@@ -25,7 +25,7 @@ class Admin_Manage_Comments_Controller extends Admin_Controller {
     db::build()
       ->delete("comments")
       ->where("state", "IN", array("deleted", "spam"))
-      ->where("updated", "<", "UNIX_TIMESTAMP() - 86400 * 7")
+      ->where("updated", "<", new Database_Expression("UNIX_TIMESTAMP() - 86400 * 7"))
       ->execute();
 
     // Redirect to the appropriate queue