Pre-Build event in WebCore.vcproj states: "set PATH=%SystemDrive%\cygwin\bin;%PATH%" This assumes Cygwin is installed on the C: drive (or rather, the main drive). However, Cygwin could be installed almost anywhere. It's probably a reasonable assumption in the general case, but it might be better to require users to declare a specific environment variable for this, or add Cygwin to their PATH variable before starting the build. There may be other instances of this in the various build and Makefiles.