Hi John, > I get the error below when trying to build clang with expensive checks. > Works fine w/o these. Is this a known problem? this is a bug in libstdc++, and has been fixed here: http://gcc.gnu.org/viewcvs?view=revision&revision=147599 If you can't pick up the fix, try compiling clang without the -fno-rtti option. Ciao, Duncan.