diff --git a/pkgs/mruby/mrblib/kernaux.rb b/pkgs/mruby/mrblib/kernaux.rb
index b959ef5..cf9cff7 100644
--- a/pkgs/mruby/mrblib/kernaux.rb
+++ b/pkgs/mruby/mrblib/kernaux.rb
@@ -25,4 +25,7 @@ module KernAux
 
   class Error < RuntimeError; end
   class AssertError < Error; end
+  class CmdlineError < Error; end
+  class InvalidNtoaBaseError < Error; end
+  class TooLongNtoaPrefixError < Error; end
 end