 <p>Guy's answer above seems to fix the problem compiling Ruby in RVM with XCode 4.2 installed completely, and removed for me to install GCC from <a href="https://github.com/kennethreitz/osx-gcc-installer" rel="nofollow">https://github.com/kennethreitz/osx-gcc-installer</a> . This is preferable for users needing to have both RVM and XCode 4.2 installed.</p>