mpl/test/set_c.cpp has been failing for all my toolsets (in both master and develop) with the same error, In file included from ..\..\../boost/mpl/set/aux_/begin_end_impl.hpp:19:0, from ..\..\../boost/mpl/set/set0.hpp:29, from ..\..\../boost/mpl/set/set0_c.hpp:18, from ..\..\../boost/mpl/set/set10_c.hpp:19, from ..\..\../boost/mpl/set/set20_c.hpp:19, from ..\..\../boost/mpl/set_c.hpp:36, from set_c.cpp:14: ..\..\../boost/mpl/set/aux_/iterator.hpp:57:1: error: no type named `base` in `struct boost::mpl::set0_c<bool>` The regression report is all green though, so it was a bit of a mystery. Turned out that I needed to run "b2 headers". So there is an MPL header that b2 misses, although I don't have time at the moment to identify which one. But I decided to report the experience anyway, in case someone runs into the same problem. :-)