diff --git a/app/assets/javascripts/discourse/widgets/topic-map.js.es6 b/app/assets/javascripts/discourse/widgets/topic-map.js.es6
index 16c78eaa2..420e45702 100644
--- a/app/assets/javascripts/discourse/widgets/topic-map.js.es6
+++ b/app/assets/javascripts/discourse/widgets/topic-map.js.es6
@@ -186,7 +186,7 @@ export default createWidget('topic-map', {
   buildKey: attrs => `topic-map-${attrs.id}`,
 
   defaultState(attrs) {
-    return { collapsed: attrs.topicPostsCount < 50 };
+    return { collapsed: (attrs.topicPostsCount || 0) < 50 };
   },
 
   html(attrs, state) {