-Ku to compile Rubygem on Windows / Ruby 1.9.3

Using Taskjuggler and I love it. On Linux I can download the latest code from the Git repo and compile to a gem exactly as directed in the docs.

However, on my Windows 7 machine, no joy.rake gem produced the error
ERROR: Ups, you have triggered a bug in TaskJuggler!
incompatible character encodings: UTF-8 and IBM437

I finally got this to work by editing C:\Ruby193\bin\rake, changing the first line from
#!C:/Ruby193/bin/ruby.exe
to
#!C:/Ruby193/bin/ruby.exe -Ku