diff --git a/app/controllers/admin/groups_controller.rb b/app/controllers/admin/groups_controller.rb
index ed4de972882..c93e287cee7 100644
--- a/app/controllers/admin/groups_controller.rb
+++ b/app/controllers/admin/groups_controller.rb
@@ -35,7 +35,6 @@ class Admin::GroupsController < Admin::AdminController
         id
       end
       invalid_users = users.reject! { |u| valid_emails[u] || valid_usernames[u] }
-      valid_users.flatten!
       group.bulk_add(valid_users) if valid_users.present?
       users_added = valid_users.count
     end