https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81221
--- Comment #2 from Jeff Hammond <jeff.science at gmail dot com> --- Thank you! Indeed, that fixes it, both when applied directly to the installed header and when integrated into a build of the latest version. $ g++-8 -std=gnu++17 -g -O3 -mtune=native -D_GLIBCXX_PARALLEL -fopenmp test.cc&& echo "SUCCESS" || echo "FAIL" SUCCESS $ g++-8 -v Using built-in specs. COLLECT_GCC=g++-8 COLLECT_LTO_WRAPPER=/opt/gcc/HEAD/bin/../libexec/gcc/x86_64-pc-linux-gnu/8.0.0/lto-wrapper Target: x86_64-pc-linux-gnu Configured with: /opt/gcc//git/configure --program-suffix=-8 --disable-multilib --enable-threads=posix --enable-checking=release --with-system-zlib --enable-__cxa_atexit --enable-languages=c,c++,fortran --with-tune=native --enable-bootstrap --enable-lto --enable-gold=yes --enable-ld=yes --prefix=/opt/gcc//HEAD : (reconfigured) /opt/gcc//git/configure --program-suffix=-8 --disable-multilib --enable-threads=posix --enable-checking=release --with-system-zlib --enable-__cxa_atexit --enable-languages=c,c++,fortran --with-tune=native --enable-bootstrap --enable-lto --enable-gold=yes --enable-ld=yes --prefix=/opt/gcc//HEAD Thread model: posix gcc version 8.0.0 20170627 (experimental) (GCC)