diff --git a/app/controllers/watchers_controller.rb b/app/controllers/watchers_controller.rb
index 0096d8ac1..e6c4d3119 100644
--- a/app/controllers/watchers_controller.rb
+++ b/app/controllers/watchers_controller.rb
@@ -55,6 +55,9 @@ class WatchersController < ApplicationController
       user_ids = params[:watcher][:user_ids] || [params[:watcher][:user_id]]
       @users = User.active.where(:id => user_ids).all
     end
+    if @users.blank?
+      render :nothing => true
+    end
   end
 
   def destroy
diff --git a/test/functional/watchers_controller_test.rb b/test/functional/watchers_controller_test.rb
index 8ec2aa112..dc72a9b6b 100644
--- a/test/functional/watchers_controller_test.rb
+++ b/test/functional/watchers_controller_test.rb
@@ -237,6 +237,13 @@ class WatchersControllerTest < ActionController::TestCase
     end
   end
 
+  def test_append_without_user_should_render_nothing
+    @request.session[:user_id] = 2
+    xhr :post, :append, :project_id => 'ecookbook'
+    assert_response :success
+    assert response.body.blank?
+  end
+
   def test_remove_watcher
     @request.session[:user_id] = 2
     assert_difference('Watcher.count', -1) do