diff --git a/slackviewer/templates/viewer.html b/slackviewer/templates/viewer.html
index 8e17c2f..714752f 100644
--- a/slackviewer/templates/viewer.html
+++ b/slackviewer/templates/viewer.html
@@ -62,7 +62,7 @@ <h3 id="mpim-title">Group Direct Messages</h3>
     <div class="messages">
         {% for message in messages %}
             {% if message.msg or message.files %}
-                {% if "Thread Reply:" in message.msg %}
+                {% if message.msg and "Thread Reply:" in message.msg %}
                     {{render_message(message, None, no_external_references, reply=True)}}
                 {% else %}
                     {{render_message(message, None, no_external_references, reply=False)}}