diff --git a/lib/pry.rb b/lib/pry.rb
index 48a7af6b..f5e84a3f 100644
--- a/lib/pry.rb
+++ b/lib/pry.rb
@@ -149,6 +149,9 @@ class Pry
   class CommandError < StandardError; end
   class NonMethodContextError < CommandError; end
 
+  # indicates obsolete API
+  class ObsoleteError < StandardError; end
+
   # This is to keep from breaking under Rails 3.2 for people who are doing that
   # IRB = Pry thing.
   module ExtendCommandBundle