Hello, After updating to Boost 1.89 I can no longer build my code that uses boost::math::zeta() with a boost::multiprecision::mpfr_float custom type (dynamic backend). The compiler fails with: static assertion failed: Your platform does not support thread_local with non-trivial types, last checked with Mingw-x64-8.1, Jan 2021. Please try a Mingw build with the POSIX threading model, see https://sourceforge.net/p/mingw-w64/bugs/527/ I use Windows 11, MSYS2 ucrt64 toolchain GCC 15.2.0 (Thread model: posix) . Boost also installed by MSYS2 ucrt64. Building from VS Code tasks with a flag -pthread Has anyone else encountered this with Boost 1.89 on MinGW-w64? Are there recommended compiler flags or things to work around it? For now I can only downgrade to Boost 1.88 - compile without problems. Best regards, Ivo. e ivo.celmans@gmail.com