I've found that type_erasure::any and process::child conflict with each other in how they use mp11 and fusion. The issue may be specific to compiling the process library on Windows as it occurs in calls through detail headers in the library that are specific to Windows, and I haven't tested on other platforms.. #include #include Order doesn't matter. 1>c:\<removed>\boost\boost\fusion\adapted\std_tuple\tag_of.hpp(38): error C2953: 'boost::mpl::sequence_tag>': class template has already been defined 1>c:\<removed>\boost\boost\mp11\mpl.hpp(155): note: see declaration of 'boost::mpl::sequence_tag>' Boost 1.67, 1.70 VS 2017 (5.9.12)