diff --git a/lib/reline.rb b/lib/reline.rb
index 191d8bb158..c27e4a380d 100644
--- a/lib/reline.rb
+++ b/lib/reline.rb
@@ -322,6 +322,7 @@ module Reline
     if ENV['RELINE_STDERR_TTY']
       $stderr.reopen(ENV['RELINE_STDERR_TTY'], 'w')
       $stderr.sync = true
+      $stderr.puts "Reline is used by #{Process.pid}"
     end
     otio = Reline::IOGate.prep