diff --git a/dediprog.c b/dediprog.c
index 58f1d43..72818ea 100644
--- a/dediprog.c
+++ b/dediprog.c
@@ -412,15 +412,15 @@
 	struct libusb_transfer *transfers[DEDIPROG_ASYNC_TRANSFERS] = { NULL, };
 	struct libusb_transfer *transfer;
 
+	if (len == 0)
+		return 0;
+
 	if ((start % chunksize) || (len % chunksize)) {
 		msg_perr("%s: Unaligned start=%i, len=%i! Please report a bug at flashrom@flashrom.org\n",
 			 __func__, start, len);
 		return 1;
 	}
 
-	if (len == 0)
-		return 0;
-
 	int command_packet_size;
 	switch (protocol()) {
 	case PROTOCOL_V1:
@@ -504,7 +504,7 @@
 	int ret;
 	/* chunksize must be 512, other sizes will NOT work at all. */
 	const unsigned int chunksize = 0x200;
-	unsigned int residue = start % chunksize ? chunksize - start % chunksize : 0;
+	unsigned int residue = start % chunksize ? min(len, chunksize - start % chunksize) : 0;
 	unsigned int bulklen;
 
 	dediprog_set_leds(LED_BUSY);