diff --git a/app/serializers/listable_topic_serializer.rb b/app/serializers/listable_topic_serializer.rb
index bf62e14f68..13a87235c1 100644
--- a/app/serializers/listable_topic_serializer.rb
+++ b/app/serializers/listable_topic_serializer.rb
@@ -27,7 +27,7 @@ class ListableTopicSerializer < BasicTopicSerializer
   has_one :last_poster, serializer: BasicUserSerializer, embed: :objects
 
   def highest_post_number
-    (scope.is_staff? && object.highest_staff_post_number) || object.highest_post_num
+    (scope.is_staff? && object.highest_staff_post_number) || object.highest_post_number
   end
 
   def liked