Hi Steven, I have been toying around with your zlib changes but I'm stuck when compiling boost trunk. I did add a rule in my user-config.jam saying: #------------------------------- # 3rd Party Libs #------------------------------- using zlib : 1.2.5 : <source>C:\chhenning\zlib\zlib-1.2.5 : <toolset>msvc ; and now when I run bjam with the following command line: bjam -j8 --toolset=msvc --without-mpi variant=debug link=static runtime-link=shared define=_CRT_NONSTDC_NO_DEPRECATE define=_CRT_SECURE_NO_DEPRECATE define=_SCL_SECURE_NO_DEPRECATE stage I get this error: Performing configuration checks - 32-bit : yes - arm : no - mips1 : no - power : no - sparc : no - x86 : yes - has_icu builds : no warning: Graph library does not contain MPI-based parallel components. note: to enable them, add "using mpi ;" to your user-config.jam C:/boost/tools/build/v2/build\targets.jam:1203: in object(ac-library)@42.match ERROR: rule "<toolset>msvc.base" unknown in module "object(ac-library)@42". C:/boost/tools/build/v2/build\targets.jam:662: in select-alternatives C:/boost/tools/build/v2/build\targets.jam:747: in generate-really C:/boost/tools/build/v2/build\targets.jam:729: in object(main-target)@1746.generate C:/boost/tools/build/v2/build\targets.jam:874: in targets.generate-from-reference C:/boost/tools/build/v2/build\ac.jam:240: in object(check-library-worker)@562.check C:/boost/tools/build/v2/kernel\modules.jam:107: in modules.call-in C:/boost/tools/build/v2/util\indirect.jam:98: in indirect.call C:/boost/tools/build/v2/build\targets.jam:1033: in evaluate-requirements C:/boost/tools/build/v2/build\targets.jam:1091: in common-properties2 C:/boost/tools/build/v2/build\targets.jam:956: in targets.common-properties C:/boost/tools/build/v2/build\targets.jam:1282: in object(typed-target)@567.generate C:/boost/tools/build/v2/build\targets.jam:757: in generate-really C:/boost/tools/build/v2/build\targets.jam:729: in object(main-target)@1735.generate C:/boost/tools/build/v2/build\targets.jam:272: in object(project-target)@560.generate C:/boost/tools/build/v2/build\targets.jam:874: in targets.generate-from-reference C:/boost/tools/build/v2/build\targets.jam:1245: in generate-dependencies C:/boost/tools/build/v2/build\targets.jam:1302: in object(alias-target-class)@108.generate C:/boost/tools/build/v2/build\targets.jam:757: in generate-really C:/boost/tools/build/v2/build\targets.jam:729: in object(main-target)@1093.generate C:/boost/tools/build/v2/build\targets.jam:874: in targets.generate-from-reference C:/boost/tools/build/v2/build\targets.jam:1245: in generate-dependencies C:/boost/tools/build/v2/build\targets.jam:1302: in object(install-target-class)@153.generate C:/boost/tools/build/v2/build\targets.jam:757: in generate-really C:/boost/tools/build/v2/build\targets.jam:729: in object(main-target)@1118.generate C:/boost/tools/build/v2/build\targets.jam:874: in targets.generate-from-reference C:/boost/tools/build/v2/build\targets.jam:1245: in generate-dependencies C:/boost/tools/build/v2/build\targets.jam:1302: in alias-target-class.generate C:/boost\boostcpp.jam:431: in build-multiple C:/boost\boostcpp.jam:393: in object(top-level-target)@160.generate C:/boost/tools/build/v2/build\targets.jam:757: in generate-really C:/boost/tools/build/v2/build\targets.jam:729: in object(main-target)@1122.generate C:/boost/tools/build/v2\build-system.jam:705: in load C:\boost\tools\build\v2/kernel\modules.jam:289: in import C:\boost\tools\build\v2/kernel/bootstrap.jam:139: in boost-build C:\boost\boost-build.jam:17: in module scope I did update the complete trunk and therefore I'm trying to rebuild the boost libs. Regards, Christian