In boost 1.35 on Linux on x86-64 an attempt to serialize any of the STL collections produces multiple definitions of implementation_level. Eventually I tracked these to the int64_t handling in collection_traits.hpp, where the following code appears: // determine if its necessary to handle (u)int64_t specifically // i.e. that its not a synonym for (unsigned) long // if there is no 64 bit int or if its the same as a long // we shouldn't define separate functions for int64 data types. #if defined(BOOST_NO_INT64_T) \ || (ULONG_MAX != 0xffffffff && ULONG_MAX == 18446744073709551615u) // 2**64 - 1 # define BOOST_NO_INTRINSIC_INT64_T #endif The bug is that the lengthy constant is just "u", and so will be compiler-truncated to unsigned int, 4 bytes on this platform, and so will fail to be equal to the 8-byte ULONG_MAX. Changing the "u" to "ul" fixes the bug. I don't know if this has already been fixed in 1.36; I don't have a copy handy. Ivan Godard