diff --git a/themes/default/templates/categories.html b/themes/default/templates/categories.html
index d638194..ad35e82 100644
--- a/themes/default/templates/categories.html
+++ b/themes/default/templates/categories.html
@@ -7,7 +7,7 @@
 {% block content_title %}
 {% endblock %}
 
-	{% for category, articles in categories | sort %}
+	{% for category, articles in categories | sort(attribute="slug") %}
 		<a class="nounderline" href="{{ SITEURL }}/{{ category.url }}" title="Permalink to {{ category|striptags }}">
 			<h1 class="category">{{ category }}</h1>
 		</a>