Created attachment 272327 [details] build log Failed with the attached output. (with Emacs24) Seems this is upstream bug page (already fixed) http://rubyforge.org/tracker/?group_id=1900&atid=7436&func=detail&aid=27152
Created attachment 272329 [details, diff] proposed patch upstream r924 seems to fix the problem. This patch is made by svn diff -r 923:924 emacs > ~/tmp/ruby-debug.patch
Thanks for the report and patch. I've fixed this by bumping the ruby-debug version to 0.10.4, which has this patch included.