diff --git a/_includes/sidebar.html b/_includes/sidebar.html
index 32ee06a..865b81a 100644
--- a/_includes/sidebar.html
+++ b/_includes/sidebar.html
@@ -12,7 +12,9 @@
       <strong>Note: </strong> {{ page.note | markdownify | remove: '<p>' | remove: '</p>' }}
     </p>
     {% endif %}
-    <p>You can also add <strong><code>{{ page.spdx-id }}</code></strong>, the standard identifier for this license, to your project's package description, if applicable. Examples: <a href="https://docs.npmjs.com/files/package.json#license">Node.js</a>, <a href="http://guides.rubygems.org/specification-reference/#license=">Ruby</a>, and <a href="http://doc.crates.io/manifest.html#package-metadata">Rust</a>.</p>
+    {% assign xgpl = false %}
+    {% if page.spdx-id contains 'GPL' %}{% assign xgpl = true %}{% endif %}
+    <p>You can also add <strong><code>{{ page.spdx-id }}</code>{% if xgpl %}+{% endif %}</strong>{% if xgpl %} (or <strong><code>{{ page.spdx-id }}</code></strong> to disallow future versions){% endif %}, the standard identifier for this license, to your project's package description, if applicable. Examples: <a href="https://docs.npmjs.com/files/package.json#license">Node.js</a>, <a href="http://guides.rubygems.org/specification-reference/#license=">Ruby</a>, and <a href="http://doc.crates.io/manifest.html#package-metadata">Rust</a>.</p>
   </div>
 
   {% if page.source %}