Can't build basic Qt project from Creator using 5.1.0 RC

I installed Qt 5.1.0 RC using the offline installer for OSX, installed to /Developer

I launched QtCreator 2.7.2 bundled with this version and created a vanilla C++ Qt GUI application.

Creator had auto-detected and auto-created a kit for this release.

When I try to build the project, I get this error which I've never seen before:

Project ERROR: Xcode is not installed in /Developer/Xcode.app/Contents/Developer. Please use xcode-select to choose Xcode installation path.
19:59:44: The process "/Developer/Qt_5_1_0_RC/5.1.0-rc1/clang_64/bin/qmake" exited with code 3.

My XCode is installed in /Applications as is the default for v 4.x.

If I switch back to my qt 5.0.1 kit, the project builds correctly.