diff --git a/KNOWNBUGS.rb b/KNOWNBUGS.rb
index b9ffabf212..5e3c5dd01f 100644
--- a/KNOWNBUGS.rb
+++ b/KNOWNBUGS.rb
@@ -13,4 +13,4 @@ assert_equal "ArgumentError", %{
   rescue ArgumentError => e
     e.class
   end
-}
+}, '[Bug #12705]'