This is a re-post of " [boost] BOOST_PP_ITERATE for huge mpl and fusion". I think problem may be that I didn't target a particular library because it happens in three. There is an undocumented hard-coded limit of 50 in MPL, Fusion, and Phoenix. I count two impls 1) has 20 elements all generated boost_1_49_0/boost/mpl/aux_/preprocessed/gcc/vector.hpp 2) stops at 50 boost_1_49_0/boost/mpl/vector/vector50.hpp I don't know if there's a way to generate more. Probably you need python. If that's the case, IMHO this should be documented so users can do it. This doesn't work: #define BOOST_MPL_CFG_NO_PREPROCESSED_HEADERS #define BOOST_MPL_LIMIT_VECTOR_SIZE 60 #include <boost/mpl/vector.hpp> boost_1_49_0/boost/mpl/vector.hpp:36:73: fatal error: boost/mpl/vector/vector60.hpp: No such file or directory Can someone please help. I've upgraded my copy of boost. I've tried figuring out how these headers work. I'm pretty sure I could fix it if I really had to by replacing the 50 in the last file with the *_SIZE. I have this ugly hack in my code to keep things working. Would someone please help?!? Acknowledging the problem would be a start. Chris