Hello, I believe there is a type conflict in boost/iostreams/detail/buffer.hpp. ------ Snippet from buffer.hpp ------ class basic_buffer { ... basic_buffer (int buffer_size); ... std::streamsize size_; }; ------ End snippet ------ Here is some example code that triggers the same warnings I was receiving: // Tested with boost 1.46.1 // Compiler Microsoft VC2010 SP1. // Compiled with cl /EHsc /W3 repro.cpp #include <boost/iostreams/copy.hpp> #include <boost/iostreams/device/array.hpp> #include <boost/iostreams/filtering_streambuf.hpp> int main (int, char *[]) { static const char b[] = { 'A', 'B', 'C' }; boost::iostreams::array_source as (b, 3); boost::iostreams::filtering_streambuf <boost::iostreams::input> in; in.push (as); // This line generates a 'std::streamsize' to 'int' warning. // See also boost/iostreams/detail/buffer.hpp boost::iostreams::copy (in, std::cout); return 0; } Perhaps the fix is as simple as s/int/std::streamsize/g within buffer.hpp. Any thoughts? Thanks, Judson