Setting RUBYLIB while debugging

Currently I have a ruby script that is normally run via a windows batch
file that has

set RUBYLIB=…
ruby …\rubyfile.rb

When I run the ruby script with rdebug I run into a problem that
required ruby files cannot be accessed from the RUBYLIB folder i.e I get
error

C:/Work/ruby/bin/rdebug:19 Uncaught exception: no such file to load –
ScriptReader

How do I get rdebug to know about the RUBYLIB folder where the
ScriptReader script lives?

David