diff --git a/lib/usb_dfu.c b/lib/usb_dfu.c
index 1357d5f..754d85a 100644
--- a/lib/usb_dfu.c
+++ b/lib/usb_dfu.c
@@ -157,7 +157,7 @@ static void usb_dfu_flash(usbd_device *usbd_dev, struct usb_setup_data *req)
 	(void)usbd_dev; // variable not used
 	(void)req; // variable not used
 	led_off(); // indicate we are processing
-	if (0 != flash_internal_write(flash_pointer, download_data, download_length, true)) { // write downloaded data
+	if (flash_internal_write(flash_pointer, download_data, download_length, true) >= download_length) { // write downloaded data
 		flash_pointer += download_length; // go to next segment
 		usb_dfu_state = STATE_DFU_DNLOAD_IDLE; // go back to idle stat to wait for next segment
 	} else { // warn about writing error