Trying to build ruby- 1.8.7 with rbenv on Mountain Lion and getting something similar to: tcltklib.c:9862: error: expected ‘;’ before ‘event’ You need to install XQuartz first and then use the following CPPFLAGS evn-var. (Also won't hurt to throw proper readline support in there while we are at it ( brew install readline first): CPPFLAGS=-I/opt/X11/include/ RUBY_CONFIGURE_OPTS=--with-readline-dir=`brew --prefix readline` rbenv install 1.8.7-p374 Hope that helps you. If anything is a future reference point to myself :P