Hi, currently it is not possible to build GCC's libjava support on Cygwin-64. The attached patch fixes the current build-problems and the most fundamental bugs on that platform. Note you must still add --enable-threads=posix to successfully build the java language support. Boot-Strapped on Cygwin-32 and Cygwin-64. OK for trunk and 4.9.1? Thanks Bernd.