I posted this to boost.user but didn't get any reply so I will try here instead. The problem (as far as I can tell) is that a buffered iostreams::stream dumps it's internal buffers every time you call seek or tell, even if you seek to the current position. You end up in this function. template<typename T, typename Tr, typename Alloc, typename Mode> typename indirect_streambuf<T, Tr, Alloc, Mode>::pos_type indirect_streambuf<T, Tr, Alloc, Mode>::seek_impl (stream_offset off, BOOST_IOS::seekdir way, BOOST_IOS::openmode which) { if (pptr() != 0) this->BOOST_IOSTREAMS_PUBSYNC(); // sync() confuses VisualAge 6. if (way == BOOST_IOS::cur && gptr()) off -= static_cast<off_type>(egptr() - gptr()); setg(0, 0, 0); setp(0, 0); return obj().seek(off, way, which, next_); } I am no expert in iostreams but I think that the naive idea would be to check if the buffer already contains the position we are searching for and if so, adjust the buffers accordingly (at least if the stream is binary). With the current implementation you can't really use buffered streams if you seek a lot in them (which, perhaps is the reason you want to use buffered streams in the first place).