diff --git a/src/helpers/Markdown.php b/src/helpers/Markdown.php
index 7c7cdb7..994cdeb 100755
--- a/src/helpers/Markdown.php
+++ b/src/helpers/Markdown.php
@@ -53,11 +53,13 @@ class Markdown extends \Parsedown
 
     private function purifyHtml($html) {
         $config = \HTMLPurifier_Config::createDefault();
+
         $config->set('HTML.Doctype', 'XHTML 1.0 Transitional');
         $config->set('HTML.Allowed', 'p,strong,em,b,a[href],i,span,ul,ol,li,cite,code,pre,br,blockquote,img');
-        $config->set('HTML.AllowedAttributes', 'src, height, width, alt, href, class');
+        $config->set('HTML.AllowedAttributes', 'src, height, width, alt, href, class, rel');
         $config->set('URI.AllowedSchemes', array('http' => true, 'https' => true, 'mailto' => true, 'ftp' => true));
         $config->set('HTML.TargetBlank', true);
+        $config->set('HTML.Nofollow', true);
 
         $purifier = new \HTMLPurifier($config);
 
diff --git a/src/templates/issue.twig b/src/templates/issue.twig
index 777cb0f..5cd9ffa 100755
--- a/src/templates/issue.twig
+++ b/src/templates/issue.twig
@@ -1,6 +1,10 @@
 {% extends "layout.twig" %}
 {% import "macros.twig" as macro %}
 
+{% block head %}
+    <link rel="canonical" href="https://github.com/matomo-org/matomo/{{ pull_request ? "pulls" : "issues" }}/{{ number|e('html_attr') }}" />
+{% endblock %}
+
 {% block title %}
     <title>{{ projectName }} {{ pull_request ? "Pull Request" : "Issue" }} #{{ number }} - {{ title }}</title>
 {% endblock %}
diff --git a/src/templates/layout.twig b/src/templates/layout.twig
index 2dc8a4b..8890b02 100644
--- a/src/templates/layout.twig
+++ b/src/templates/layout.twig
@@ -7,6 +7,7 @@
     <link href="/css/style.css" rel="stylesheet">
 
     {% block head %}
+        <link rel="canonical" href="https://github.com/matomo-org/matomo/issues/" />
     {% endblock %}
 
     {% block title %}
diff --git a/src/templates/page.twig b/src/templates/page.twig
index dd156d5..a640323 100644
--- a/src/templates/page.twig
+++ b/src/templates/page.twig
@@ -9,6 +9,8 @@
     {% if currentPage != numPages %}
         <link rel="next" href="{{ path_for('page', [], { 'page': nextPage }) }}"/>
     {% endif %}
+
+    <link rel="canonical" href="https://github.com/matomo-org/matomo/issues/" />
 {% endblock %}
 
 {% block content %}