I see a bunch of CI failures https://apolukhin.github.io/en/developer.html for different versions of MSVC. There are some complains on 'cl': compile-c-c++ ..\..\..\bin.v2\libs\type_index\test\track_13621.test\msvc-9.0\release\threading-multi\track_13621.obj 'cl' is not recognized as an internal or external command, operable program or batch file. call "..\..\..\bin.v2\standalone\msvc\msvc-9.0\msvc-setup.bat" amd64 >nul cl /Zm800 -nologo "track_13621.cpp" -Fo"..\..\..\bin.v2\libs\type_index\test\track_13621.test\msvc-9.0\release\threading-multi\track_13621.obj" -TP -DBOOST_TRAVISCI_BUILD /wd4675 /EHs /GR /O2 /Ob2 /W3 /MD /Zc:forScope /Zc:wchar_t /favor:blend -c -DBOOST_ALL_NO_LIB=1 -DNDEBUG "-I..\..\.." ...failed compile-c-c++ ..\..\..\bin.v2\libs\type_index\test\track_13621.test\msvc-9.0\release\threading-multi\track_13621.obj... Is that a known issue?