While trying to run the tests for the MS vc6 compiler I found that the build is aborted when trying to build the serialization test. When I put toolset::require-boost-spirit-support into the Jamfile the build is correctly skipped instead of aborted. My version below: rule sc-serialization-test ( name : requirements * ) { return [ run $(name).cpp <lib>../../test/build/boost_unit_test_framework <lib>../../serialization/build/boost_serialization : : : toolset::require-boost-spirit-support ] ; } Since I do not yet know boost.build very good, I cannot tell if this works by accident or if it is correct. I figured this out by comparison with similar cases from other libs. I suspect this issue is not specific to the vc6 build, but might fail in other cases too. If there are no objections I will check this into CVS. (After the release branch.) Roland