In fact, POSIX has exactly the same text in fflush and fclose in the RETURN VALUE section (except the "it shall set the error indicator for the stream" part simply because the stream will be closed). It also says "The fclose() function shall cause the stream pointed to by stream to be flushed and the associated file to be closed". It does not say anything about not returning EOF if an error has happened in the flushing part. And in fact, some of the ERRORS in the POSIX page are about flushing failing.