diff --git a/app/helpers/application_helper.rb b/app/helpers/application_helper.rb
index a1d989e25..722bb5d9c 100644
--- a/app/helpers/application_helper.rb
+++ b/app/helpers/application_helper.rb
@@ -75,7 +75,7 @@ module ApplicationHelper
     end
 
     css_classes += " #{options[:class]}" if css_classes && options[:class].present?
-    url ? link_to(name, url, :class => css_classes) : name
+    url ? link_to(name, url, :class => css_classes, :data => options[:data]) : name
   end
 
   # Displays a link to edit group page if current user is admin
@@ -1275,7 +1275,10 @@ module ApplicationHelper
           elsif sep == "@"
             name = remove_double_quotes(identifier)
             u = User.visible.find_by("LOWER(login) = :s AND type = 'User'", :s => name.downcase)
-            link = link_to_user(u, :only_path => only_path, :class => 'user-mention', :mention => true) if u
+            if u && obj && !obj.visible?(u)
+              data = {warning_tooltip: l(:error_not_mentioned)}
+            end
+            link = link_to_user(u, :only_path => only_path, :class => 'user-mention', :mention => true, :data => data) if u
           end
         end
         (leading + (link || "#{project_prefix}#{prefix}#{repo_prefix}#{sep}#{identifier}#{comment_suffix}"))
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 3f60e9e73..d79bf486f 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -244,6 +244,7 @@ en:
   error_invalid_size_parameter: "Invalid size parameter"
   error_attachment_not_found: "Attachment %{name} not found"
   error_invalid_authenticity_token: "Invalid form authenticity token."
+  error_not_mentioned: "You cannot mention this user because they do not have access rights."
   error_query_statement_invalid: "An error occurred while executing the query and has been logged. Please report this error to your Redmine administrator."
 
   mail_subject_lost_password: "Your %{value} password"
diff --git a/public/javascripts/application.js b/public/javascripts/application.js
index a183a2777..97b24cbb9 100644
--- a/public/javascripts/application.js
+++ b/public/javascripts/application.js
@@ -1121,6 +1121,21 @@ $(function () {
       at: "center top"
     }
   });
+
+  $("[data-warning-tooltip]:not(.no-tooltip)").tooltip({
+    items: '[data-warning-tooltip]',
+    content: function() {
+      return $(this).data('warning-tooltip');
+    },
+    tooltipClass: 'warning',
+    show: {
+      delay: 400
+    },
+    position: {
+      my: "center bottom-5",
+      at: "center top"
+    }
+  });
 });
 
 function inlineAutoComplete(element) {
diff --git a/public/stylesheets/application.css b/public/stylesheets/application.css
index f8e11b050..20a629d12 100644
--- a/public/stylesheets/application.css
+++ b/public/stylesheets/application.css
@@ -1573,6 +1573,11 @@ td.gantt_selected_column .gantt_hdr,.gantt_selected_column_container {
   box-shadow: none;
   white-space: pre-wrap;
 }
+.ui-tooltip.warning {
+  background-color: #F3EDD1;
+  border-color: #eadbbc;
+  color: #A6750C;
+}
 
 /***** Icons *****/
 .icon {
diff --git a/test/helpers/application_helper_test.rb b/test/helpers/application_helper_test.rb
index 180066b17..99ff26f06 100644
--- a/test/helpers/application_helper_test.rb
+++ b/test/helpers/application_helper_test.rb
@@ -580,6 +580,18 @@ class ApplicationHelperTest < Redmine::HelperTest
     end
   end
 
+  def test_mention_link_to_users_who_are_not_authorised_to_view_the_object
+    set_language_if_valid 'en'
+    with_settings :text_formatting => 'textile' do
+      issue = Issue.find(4)
+      assert_not issue.visible?(User.find(3))
+      assert_equal "<p>#{link_to_user(User.find(3), only_path: true, class: 'user-mention', mention: true, data: {warning_tooltip: 'You cannot mention this user because they do not have access rights.'})}</p>", textilizable("@#{User.find(3).login}", :object => issue)
+
+      journal = Journal.find(2)
+      assert_equal '<p><a href="#note-2">#note-2</a></p>', textilizable('#note-2', :object => journal)
+    end
+  end
+
   def test_link_to_note_within_the_same_page
     with_settings :text_formatting => 'textile' do
       issue = Issue.find(1)