I agree with the objection raised by the original poster. The assertion in archive/basic_binary_oprimitive.hpp should more properly be an exception. Standard library ostreams fail silently when in an error state (including std::ofstreams that fail to open a file). Writing a std::string, int, double, or any other data to a default-constructed std::ostream is a no-op. The only exception to this appears to be writing a boost::serialization archive to a std::ostream, which under some circumstances fails with an abort when "assert(os.good());" fails in archive/basic_binary_oprimitive.hpp. There is also an exception thrown based on the state of the ostream in the same function as this assertion. The user can choose to catch this if she decides that the default std::ostream failure policy (a no-op) is acceptible. By putting the assertion in there, you force the user to always have a valid, writable std::ostream, which is precisely the opposite of what the user expects from years of using std::ostreams.