diff --git a/include/libcasio/stream.h b/include/libcasio/stream.h
index a27bd7d..a6e794c 100644
--- a/include/libcasio/stream.h
+++ b/include/libcasio/stream.h
@@ -102,7 +102,7 @@ typedef int casio_stream_settm_t
 
 typedef ssize_t casio_stream_read_t
 	OF((void *, unsigned char *, size_t));
-typedef int casio_stream_write_t
+typedef ssize_t casio_stream_write_t
 	OF((void *, const unsigned char *, size_t));
 typedef int casio_stream_seek_t
 	OF((void *, casio_off_t *, casio_whence_t));
@@ -362,7 +362,7 @@ CASIO_EXTERN int   CASIO_EXPORT casio_get_lasterr
 CASIO_EXTERN ssize_t CASIO_EXPORT casio_read
 	OF((casio_stream_t *casio__stream,
 		void *casio__dest, size_t casio__size));
-CASIO_EXTERN int CASIO_EXPORT casio_write
+CASIO_EXTERN ssize_t CASIO_EXPORT casio_write
 	OF((casio_stream_t *casio__stream,
 		const void *casio__data, size_t casio__size));
 
diff --git a/lib/file/file.h b/lib/file/file.h
index 30bc53b..0e5f85d 100644
--- a/lib/file/file.h
+++ b/lib/file/file.h
@@ -58,7 +58,8 @@
 /* Write. */
 
 # define  WRITE(CASIO__BUF, CASIO__SZ) { \
-	int WRITE_err = casio_write(buffer, (CASIO__BUF), (CASIO__SZ)); \
+	ssize_t WRITE_ssize = casio_write(buffer, (CASIO__BUF), (CASIO__SZ)); \
+	int WRITE_err = WRITE_ssize < 0 ? -WRITE_ssize : 0; \
 	if (WRITE_err) return (WRITE_err); }
 # define DWRITE(CASIO__OBJECT) \
 	WRITE(&(CASIO__OBJECT), sizeof(CASIO__OBJECT))
diff --git a/lib/link/seven/dataflow.c b/lib/link/seven/dataflow.c
index ab158df..0ff5e51 100644
--- a/lib/link/seven/dataflow.c
+++ b/lib/link/seven/dataflow.c
@@ -167,7 +167,8 @@ int CASIO_EXPORT casio_seven_get_buffer(casio_link_t *handle,
 			msg((ll_info, "buffer too full, should be emptied"));
 
 			/* Empty the buffer in the stream. */
-			buf_err = casio_write(buffer, buf, ps);
+			ssize_t ssize = casio_write(buffer, buf, ps);
+			buf_err = ssize < 0 ? -ssize : 0;
 			if (buf_err) { err = casio_error_nowrite; goto fail; }
 
 			/* Reset the pointer. */
diff --git a/lib/link/seven/datastream.c b/lib/link/seven/datastream.c
index 2af1a54..11b5862 100644
--- a/lib/link/seven/datastream.c
+++ b/lib/link/seven/datastream.c
@@ -149,17 +149,18 @@ fail:
  *	@return				the error code (0 if ok).
  */
 
-CASIO_LOCAL int casio_seven_data_write(seven_data_cookie_t *cookie,
+CASIO_LOCAL ssize_t casio_seven_data_write(seven_data_cookie_t *cookie,
 	const unsigned char *data, size_t size)
 {
 	int err; size_t tocopy, lastlimit;
 	casio_link_t *handle = cookie->_link;
+	size_t writtensize = 0;
 
 	/* Check if the stream is faulty, or if we have already finished. */
 	if (cookie->_faulty)
-		return (casio_error_nowrite);
+		return -(casio_error_nowrite);
 	if (cookie->_id > cookie->_total)
-		return (casio_error_eof);
+		return -(casio_error_eof);
 
 	/* Current packet management. */
 	if (cookie->_pos || size < BUFSIZE) {
@@ -171,13 +172,14 @@ CASIO_LOCAL int casio_seven_data_write(seven_data_cookie_t *cookie,
 		memcpy(cookie->_current, data, tocopy);
 		data += tocopy; size -= tocopy;
 		cookie->_pos += tocopy;
+		writtensize += tocopy;
 
 		/* Check if the current packet is full. */
 		if (cookie->_id == cookie->_total) {
 			if (cookie->_pos < cookie->_lastsize)
-				return (0);
+				return (writtensize);
 		} else if (cookie->_pos < BUFSIZE - 1)
-			return (0);
+			return (writtensize);
 
 		/* Send the packet. */
 		if (cookie->_id == 1 && cookie->_disp)
@@ -198,14 +200,14 @@ CASIO_LOCAL int casio_seven_data_write(seven_data_cookie_t *cookie,
 		if (err) goto fail;
 		if (cookie->_disp) (*cookie->_disp)(cookie->_disp_cookie,
 			cookie->_id, cookie->_total);
-		data += BUFSIZE; size -= BUFSIZE; cookie->_id++;
+		data += BUFSIZE; size -= BUFSIZE; cookie->_id++; writtensize += BUFSIZE;
 	}
 
 	/* Copy the last bytes of the call. */
 	lastlimit = cookie->_id == cookie->_total ? cookie->_lastsize : BUFSIZE;
 	tocopy = lastlimit; if (tocopy > size) tocopy = size;
 	memcpy(cookie->_current, data, tocopy);
-	cookie->_pos = tocopy; size -= tocopy;
+	cookie->_pos = tocopy; size -= tocopy; writtensize += tocopy;
 
 	/* Send the last packet if required. */
 	if (tocopy == lastlimit) {
@@ -220,14 +222,14 @@ CASIO_LOCAL int casio_seven_data_write(seven_data_cookie_t *cookie,
 	/* Check if there are still some bytes left
 	 * (bytes after the last packet, means the announced size
 	 *  was too small). */
-	if (size) return (casio_error_nowrite);
+	if (size) return -(casio_error_nowrite);
 
 	/* Everything went well! :) */
-	return (0);
+	return (writtensize);
 fail:
 	/* XXX: tell the distant device we have a problem? */
 	cookie->_faulty = 1;
-	return (err);
+	return -(err);
 }
 
 /**
@@ -286,11 +288,13 @@ CASIO_LOCAL int casio_seven_data_close(seven_data_cookie_t *cookie)
 		 * go directly to the end. */
 		memset(zeroes, 0, BUFSIZE);
 		for (; left >= BUFSIZE; left -= BUFSIZE) {
-			if ((err = casio_seven_data_write(cookie, zeroes, BUFSIZE)))
+			ssize_t ssize = casio_seven_data_write(cookie, zeroes, BUFSIZE);
+			if ((err = ssize < 0 ? -ssize : 0))
 				goto fail;
 		}
 
-		err = casio_seven_data_write(cookie, zeroes, left);
+		ssize_t ssize = casio_seven_data_write(cookie, zeroes, left);
+		err = ssize < 0 ? -ssize : 0;
 	}
 
 	err = 0;
diff --git a/lib/link/seven/scsi.c b/lib/link/seven/scsi.c
index a8af9b8..2db73f1 100644
--- a/lib/link/seven/scsi.c
+++ b/lib/link/seven/scsi.c
@@ -202,11 +202,12 @@ CASIO_LOCAL ssize_t seven_scsi_read(seven_scsi_cookie_t *cookie,
 	return copiedsize;
 }
 
-CASIO_LOCAL int seven_scsi_write(seven_scsi_cookie_t *cookie,
+CASIO_LOCAL ssize_t seven_scsi_write(seven_scsi_cookie_t *cookie,
 	unsigned char const *buffer, size_t size)
 {
 	casio_scsi_t scsi;
 	int err;
+	size_t writtensize = 0;
 
 	do {
 		casio_uint16_t activity;
@@ -229,7 +230,7 @@ CASIO_LOCAL int seven_scsi_write(seven_scsi_cookie_t *cookie,
 			scsi.casio_scsi_data_len = 16;
 
 			if ((err = casio_scsi_request(cookie->stream, &scsi)))
-				return (err);
+				return -(err);
 
 #if 0
 			activity = (poll_data[10] << 8) | poll_data[11];
@@ -264,14 +265,15 @@ CASIO_LOCAL int seven_scsi_write(seven_scsi_cookie_t *cookie,
 			scsi.casio_scsi_data_len = to_send;
 
 			if ((err = casio_scsi_request(cookie->stream, &scsi)))
-				return (err);
+				return -(err);
 
 			buffer += to_send;
 			size -= to_send;
+			writtensize += to_send;
 		}
 	} while (size);
 
-	return (0);
+	return (writtensize);
 }
 
 /* ---
diff --git a/lib/link/seven/send.c b/lib/link/seven/send.c
index 9eb4892..0912f2e 100644
--- a/lib/link/seven/send.c
+++ b/lib/link/seven/send.c
@@ -91,7 +91,8 @@ CASIO_LOCAL int casio_seven_send_buf(casio_link_t *handle,
 		}
 
 		/* send prepared packet */
-		err = casio_write(handle->casio_link_stream, buf, bufsize);
+		ssize_t ssize = casio_write(handle->casio_link_stream, buf, bufsize);
+		err = ssize < 0 ? -ssize : 0;
 		if (err) return (err);
 
 		/* set wasreset for logging */
diff --git a/lib/mcsfile/mcsfile.h b/lib/mcsfile/mcsfile.h
index 46d39f5..59990e7 100644
--- a/lib/mcsfile/mcsfile.h
+++ b/lib/mcsfile/mcsfile.h
@@ -57,7 +57,8 @@
 /* Write. */
 
 # define  WRITE(CASIO__BUF, CASIO__SZ) { \
-	int WRITE_err = casio_write(buffer, (CASIO__BUF), (CASIO__SZ)); \
+	ssize_t WRITE_ssize = casio_write(buffer, (CASIO__BUF), (CASIO__SZ)); \
+	int WRITE_err = WRITE_ssize < 0 ? -WRITE_ssize : 0; \
 	if (WRITE_err) return (WRITE_err); }
 # define DWRITE(CASIO__OBJECT) \
 	WRITE(&(CASIO__OBJECT), sizeof(CASIO__OBJECT))
diff --git a/lib/stream/builtin/file.c b/lib/stream/builtin/file.c
index ea3a1ea..605485f 100644
--- a/lib/stream/builtin/file.c
+++ b/lib/stream/builtin/file.c
@@ -126,10 +126,10 @@ CASIO_LOCAL ssize_t casio_file_read(file_cookie_t *cookie,
  *	@arg	cookie		the cookie.
  *	@arg	data		the source
  *	@arg	size		the source size
- *	@return				the error code (0 if ok)
+ *	@return				the size written if > 0, or if < 0 the error code is -[returned value].
  */
 
-CASIO_LOCAL int casio_file_write(file_cookie_t *cookie,
+CASIO_LOCAL ssize_t casio_file_write(file_cookie_t *cookie,
 	const unsigned char *data, size_t size)
 {
 	size_t sent;
@@ -145,7 +145,7 @@ CASIO_LOCAL int casio_file_write(file_cookie_t *cookie,
 			/* End of file (EOF). */
 
 			msg((ll_error, "encountered an end of file"));
-			return (casio_error_eof);
+			return -(casio_error_eof);
 
 		case EINTR: /* alarm */
 		case ETIMEDOUT:
@@ -155,20 +155,20 @@ CASIO_LOCAL int casio_file_write(file_cookie_t *cookie,
 			/* Timeout error. */
 
 			msg((ll_error, "timeout received"));
-			return (casio_error_timeout);
+			return -(casio_error_timeout);
 
 		case ENODEV:
 			/* Device disconnected. */
 
 			msg((ll_fatal, "calculator was disconnected"));
-			return (casio_error_nocalc);
+			return -(casio_error_nocalc);
 
 		default:
 			msg((ll_fatal, "errno was %d: %s", errno, strerror(errno)));
-			return (casio_error_unknown);
+			return -(casio_error_unknown);
 	}
 
-	return (0);
+	return sent;
 }
 
 /**
diff --git a/lib/stream/builtin/libusb/libusb.h b/lib/stream/builtin/libusb/libusb.h
index 0cd1a10..a0d5662 100644
--- a/lib/stream/builtin/libusb/libusb.h
+++ b/lib/stream/builtin/libusb/libusb.h
@@ -61,7 +61,7 @@ CASIO_EXTERN int CASIO_EXPORT casio_libusb_settm
 CASIO_EXTERN ssize_t CASIO_EXPORT casio_libusb_read
 	OF((cookie_libusb_t *casio__cookie,
 		unsigned char *casio__dest, size_t casio__size));
-CASIO_EXTERN int CASIO_EXPORT casio_libusb_write
+CASIO_EXTERN ssize_t CASIO_EXPORT casio_libusb_write
 	OF((cookie_libusb_t *casio__cookie,
 		const unsigned char *casio__data, size_t casio__size));
 
diff --git a/lib/stream/builtin/libusb/write.c b/lib/stream/builtin/libusb/write.c
index 8f36f37..c24e4a6 100644
--- a/lib/stream/builtin/libusb/write.c
+++ b/lib/stream/builtin/libusb/write.c
@@ -26,10 +26,10 @@
  *	@arg	cookie		the cookie.
  *	@arg	data		the source.
  *	@arg	size		the source size.
- *	@return				the error code (0 if ok).
+ *	@return				the size written if > 0, or if < 0 the error code is -[returned value].
  */
 
-int CASIO_EXPORT casio_libusb_write(cookie_libusb_t *cookie,
+ssize_t CASIO_EXPORT casio_libusb_write(cookie_libusb_t *cookie,
 	const unsigned char *data, size_t size)
 {
 	int sent, libusberr;
@@ -44,15 +44,15 @@ int CASIO_EXPORT casio_libusb_write(cookie_libusb_t *cookie,
 		case LIBUSB_ERROR_PIPE:
 		case LIBUSB_ERROR_NO_DEVICE:
 			msg((ll_error, "The calculator is not here anymore :("));
-			return (casio_error_nocalc);
+			return -(casio_error_nocalc);
 
 		default:
 			msg((ll_fatal, "libusb error was %d: %s", libusberr,
 				libusb_strerror(libusberr)));
-			return (casio_error_unknown);
+			return -(casio_error_unknown);
 	}
 
-	return (0);
+	return (sent);
 }
 
 #endif
diff --git a/lib/stream/builtin/memory.c b/lib/stream/builtin/memory.c
index d7a3166..5614882 100644
--- a/lib/stream/builtin/memory.c
+++ b/lib/stream/builtin/memory.c
@@ -63,25 +63,25 @@ CASIO_LOCAL ssize_t casio_memory_read(void *vcookie, unsigned char *dest, size_t
  *	@arg	vcookie		the cookie (uncasted).
  *	@arg	data		the data pointer.
  *	@arg	size		the data size.
- *	@return				the error code (0 if ok).
+ *	@return				the size written if > 0, or if < 0 the error code is -[returned value].
  */
 
-CASIO_LOCAL int casio_memory_write(void *vcookie, const unsigned char *data,
+CASIO_LOCAL ssize_t casio_memory_write(void *vcookie, const unsigned char *data,
 	size_t size)
 {
 	memory_cookie_t *cookie = (void*)vcookie;
 
 	if (((size_t)-1 - cookie->_offset) < size) /* overflow */
-		return (casio_error_write);
+		return -(casio_error_write);
 	if (cookie->_offset + (casio_off_t)size > cookie->_size) {
 		cookie->_offset = cookie->_size - 1;
-		return (casio_error_eof);
+		return -(casio_error_eof);
 	}
 
 	memcpy(&cookie->_memory[cookie->_offset], data, size);
 	cookie->_offset += size;
 
-	return (0);
+	return (size);
 }
 
 /**
diff --git a/lib/stream/builtin/streams/streams.h b/lib/stream/builtin/streams/streams.h
index 9f077f1..cdea0e2 100644
--- a/lib/stream/builtin/streams/streams.h
+++ b/lib/stream/builtin/streams/streams.h
@@ -54,7 +54,7 @@ CASIO_EXTERN int CASIO_EXPORT casio_streams_settm
 CASIO_EXTERN ssize_t CASIO_EXPORT casio_streams_read
 	OF((streams_cookie_t *casio__cookie,
 		unsigned char *casio__dest, size_t casio__size));
-CASIO_EXTERN int CASIO_EXPORT casio_streams_write
+CASIO_EXTERN ssize_t CASIO_EXPORT casio_streams_write
 	OF((streams_cookie_t *casio__cookie,
 		const unsigned char *casio__data, size_t casio__size));
 
diff --git a/lib/stream/builtin/streams/write.c b/lib/stream/builtin/streams/write.c
index 2388826..8f2d19d 100644
--- a/lib/stream/builtin/streams/write.c
+++ b/lib/stream/builtin/streams/write.c
@@ -26,13 +26,14 @@
  *	@arg	cookie		the cookie.
  *	@arg	data		the source.
  *	@arg	size		the source size.
- *	@return				the error (0 if ok).
+ *	@return				the size written if > 0, or if < 0 the error code is -[returned value].
  */
 
-int CASIO_EXPORT casio_streams_write(streams_cookie_t *cookie,
+ssize_t CASIO_EXPORT casio_streams_write(streams_cookie_t *cookie,
 	const unsigned char *data, size_t size)
 {
 	int fd = cookie->_writefd;
+	size_t writtensize = 0;
 
 	/* Send. */
 
@@ -40,19 +41,20 @@ int CASIO_EXPORT casio_streams_write(streams_cookie_t *cookie,
 		ssize_t wr = write(fd, data, size);
 		if (wr < 0) break;
 		size -= (size_t)wr;
+		writtensize += (size_t)wr;
 	}
 
 	/* Be sure it's written, or check the error. */
 
 	if (size) switch (errno) {
 		case ENODEV:
-			return (casio_error_nocalc);
+			return -(casio_error_nocalc);
 		default:
 			msg((ll_fatal, "errno was %d: %s", errno, strerror(errno)));
-			return (casio_error_unknown);
+			return -(casio_error_unknown);
 	}
 
-	return (0);
+	return (writtensize);
 }
 
 #endif
diff --git a/lib/stream/builtin/windows/windows.h b/lib/stream/builtin/windows/windows.h
index 05b5eea..839c4b1 100644
--- a/lib/stream/builtin/windows/windows.h
+++ b/lib/stream/builtin/windows/windows.h
@@ -53,7 +53,7 @@ CASIO_EXTERN int CASIO_EXPORT casio_windows_settm
 
 CASIO_EXTERN ssize_t CASIO_EXPORT casio_windows_read
 	OF((win_cookie_t *cookie, unsigned char *dest, size_t size));
-CASIO_EXTERN int CASIO_EXPORT casio_windows_write
+CASIO_EXTERN ssize_t CASIO_EXPORT casio_windows_write
 	OF((win_cookie_t *cookie, const unsigned char *data, size_t size));
 
 /* Seek callback. */
diff --git a/lib/stream/builtin/windows/write.c b/lib/stream/builtin/windows/write.c
index 6092959..6b47ce4 100644
--- a/lib/stream/builtin/windows/write.c
+++ b/lib/stream/builtin/windows/write.c
@@ -26,13 +26,14 @@
  *	@arg	cookie		the cookie.
  *	@arg	data		the source
  *	@arg	size		the source size
- *	@return				the error code (0 if ok).
+ *	@return				the size written if > 0, or if < 0 the error code is -[returned value].
  */
 
-int CASIO_EXPORT casio_windows_write(win_cookie_t *cookie,
+ssize_t CASIO_EXPORT casio_windows_write(win_cookie_t *cookie,
 	const unsigned char *data, size_t size)
 {
 	BOOL wsuccess, werr;
+	size_t writtensize = 0;
 
 	/* Make the I/O request. */
 
@@ -49,6 +50,7 @@ int CASIO_EXPORT casio_windows_write(win_cookie_t *cookie,
 
 		data += wrt;
 		size -= wrt;
+		writtensize += wrt;
 	} while (size);
 
 	/* Check the error. */
@@ -56,14 +58,14 @@ int CASIO_EXPORT casio_windows_write(win_cookie_t *cookie,
 	if (!wsuccess) switch ((werr = GetLastError())) {
 		case ERROR_DEV_NOT_EXIST:
 			msg((ll_error, "Device has been disconnected!"));
-			return (casio_error_nocalc);
+			return -(casio_error_nocalc);
 
 		default:
 			msg((ll_fatal, "Encountered error 0x%08lx", werr));
-			return (casio_error_unknown);
+			return -(casio_error_unknown);
 	}
 
-	return (0);
+	return (writtensize);
 }
 
 #endif
diff --git a/lib/stream/write.c b/lib/stream/write.c
index 128a8ed..4f0be6e 100644
--- a/lib/stream/write.c
+++ b/lib/stream/write.c
@@ -25,32 +25,38 @@
  *	@arg	stream		the stream to write to.
  *	@arg	data		the data to write.
  *	@arg	size		the amount of bytes to write.
- *	@return				the error code (0 if ok).
+ *	@return				the size written if > 0, or if < 0 the error code is -[returned value].
  */
 
-int CASIO_EXPORT casio_write(casio_stream_t *stream,
+ssize_t CASIO_EXPORT casio_write(casio_stream_t *stream,
 	const void *data, size_t size)
 {
-	int err;
+	int err = casio_error_ok;
+	ssize_t ssize = 0;
 
 	/* check if we can write */
-	failure(~stream->casio_stream_mode & CASIO_OPENMODE_WRITE,
-		casio_error_write)
+	failure(~stream->casio_stream_mode & CASIO_OPENMODE_WRITE, 
+		casio_error_write);
 
 	/* write */
-	if (!size) return (0);
-	err = (*getcb(stream, write))(stream->casio_stream_cookie, data, size);
-	if (err) {
-		msg((ll_error, "Stream writing failure: %s", casio_strerror(err)));
+	if (size == 0) {
+		return (0);
+	}
+	ssize = (*getcb(stream, write))(stream->casio_stream_cookie, data, size);
+	
+	if (ssize < 0) {
+		err = -ssize;
+		msg((ll_error, "Stream reading failure: %s", casio_strerror(err)));
 		goto fail;
 	}
 
 	/* move the cursor and return */
-	stream->casio_stream_offset += size;
-	err = 0;
+	if(ssize >= 0) {
+		stream->casio_stream_offset += size;
+	}
 fail:
 	stream->casio_stream_lasterr = err;
-	return (err);
+	return ssize;
 }
 
 /**
@@ -66,5 +72,6 @@ int CASIO_EXPORT casio_write_char(casio_stream_t *stream, int car)
 {
 	unsigned char ccar = car;
 
-	return (casio_write(stream, &ccar, 1));
+	ssize_t ssize = casio_write(stream, &ccar, 1);
+	return (ssize < 0 ? (int)-ssize : 0);
 }