diff --git a/templates/mailing_list/emails.html b/templates/mailing_list/emails.html
index 84cc3d9..0214e3a 100644
--- a/templates/mailing_list/emails.html
+++ b/templates/mailing_list/emails.html
@@ -8,10 +8,10 @@
         <summary>Filters</summary>
         
         <form action="" method="get">
-            {% for tag in tags %}
+            {% for tag in tags.keys()|sort %}
                 <div class="tag">
                     <b>{{ tag }}:</b>
-                    {% for value in tags[tag] %}
+                    {% for value in tags[tag]|sort %}
                         <label><input type="checkbox" name="{{ tag }}" value="{{ value }}" {{ 'checked' if value in query_tags[tag] }} /> {{ value }}</label>
                     {% endfor %}
                 </div>
diff --git a/web.py b/web.py
index eae3fc6..d3c7cbd 100644
--- a/web.py
+++ b/web.py
@@ -777,15 +777,14 @@ def threads(repository):
         
         thread_date, thread_time, thread_id, thread_title = obj.name.split(' ', 3)
         
-        thread_tags = {}
         try:
             thread_tags = parse_thread_tags(obj['tags'].data.decode('UTF-8'))
             
             # Collect tags for filters
             for k, v in thread_tags.items():
-                tags[k] = tags.get(k, []) + v
+                tags[k] = tags.get(k, set()).union(v)
         except:
-            pass
+            thread_tags = {}
         
         # Check if we should filter out this thread from the list
         keep = True