diff --git a/templates/cave.html b/templates/cave.html
index afc916f..c192af0 100644
--- a/templates/cave.html
+++ b/templates/cave.html
@@ -527,7 +527,7 @@ div#scene {
     <p><a href="https://aardgoose.github.io/CaveView.js/">CaveView</a> display of the .3d file is temporarily disabled while we fix things (Nov.2021). See <a href="/handbook/computing/todo.html">/handbook/computing/todo.html</a>.
     <a href="/survexfile">All survex files</a> &nbsp;&nbsp;&nbsp;
     <a href="{% if cave.kataster_number %}{% url "cave3d" cave.kataster_number %}{% else %}{% url "cave3d" cave.unofficial_number %}{% endif %}">3d file download</a>&nbsp;&nbsp;&nbsp;
-    <a href="{% url "survexcavessingle" cave.kataster_number %}">This survex file</a> &nbsp;&nbsp;&nbsp;
+    <a href="{% if cave.kataster_number %}{% url "survexcavessingle" cave.kataster_number %}">This survex file</a> &nbsp;&nbsp;&nbsp;{% endif %}">
     
     <div id='scene'></div>
 {% endif %}