diff --git a/src/storage.cr b/src/storage.cr
index 2f01863..4511255 100644
--- a/src/storage.cr
+++ b/src/storage.cr
@@ -467,6 +467,8 @@ class Storage
   end
 
   # Limit mark targets with given arguments
+  # They should be checked again if they are really gone,
+  #   since they would be available which are renamed or moved
   def mark_unavailable(ids_candidates : Array(String),
                        titles_candidates : Array(String))
     MainFiber.run do