diff --git a/mavlink/include/mavlink/v1.0/checksum.h b/mavlink/include/mavlink/v1.0/checksum.h
index 948e080a14..7d9b6ac0c7 100644
--- a/mavlink/include/mavlink/v1.0/checksum.h
+++ b/mavlink/include/mavlink/v1.0/checksum.h
@@ -73,7 +73,7 @@ static inline uint16_t crc_calculate(const uint8_t* pBuffer, uint16_t length)
  * @param data new bytes to hash
  * @param crcAccum the already accumulated checksum
  **/
-static inline void crc_accumulate_buffer(uint16_t *crcAccum, const char *pBuffer, uint8_t length)
+static inline void crc_accumulate_buffer(uint16_t *crcAccum, const char *pBuffer, uint16_t length)
 {
 	const uint8_t *p = (const uint8_t *)pBuffer;
 	while (length--) {
diff --git a/mavlink/include/mavlink/v1.0/mavlink_helpers.h b/mavlink/include/mavlink/v1.0/mavlink_helpers.h
index 96672f847f..1639a830bb 100644
--- a/mavlink/include/mavlink/v1.0/mavlink_helpers.h
+++ b/mavlink/include/mavlink/v1.0/mavlink_helpers.h
@@ -73,7 +73,6 @@ MAVLINK_HELPER uint16_t mavlink_finalize_message_chan(mavlink_message_t* msg, ui
 #endif
 {
 	// This code part is the same for all messages;
-	uint16_t checksum;
 	msg->magic = MAVLINK_STX;
 	msg->len = length;
 	msg->sysid = system_id;
@@ -81,12 +80,13 @@ MAVLINK_HELPER uint16_t mavlink_finalize_message_chan(mavlink_message_t* msg, ui
 	// One sequence number per component
 	msg->seq = mavlink_get_channel_status(chan)->current_tx_seq;
 	mavlink_get_channel_status(chan)->current_tx_seq = mavlink_get_channel_status(chan)->current_tx_seq+1;
-	checksum = crc_calculate((uint8_t*)&msg->len, length + MAVLINK_CORE_HEADER_LEN);
+	msg->checksum = crc_calculate(((const uint8_t*)(msg)) + 3, MAVLINK_CORE_HEADER_LEN);
+	crc_accumulate_buffer(&msg->checksum, _MAV_PAYLOAD(msg), msg->len);
 #if MAVLINK_CRC_EXTRA
-	crc_accumulate(crc_extra, &checksum);
+	crc_accumulate(crc_extra, &msg->checksum);
 #endif
-	mavlink_ck_a(msg) = (uint8_t)(checksum & 0xFF);
-	mavlink_ck_b(msg) = (uint8_t)(checksum >> 8);
+	mavlink_ck_a(msg) = (uint8_t)(msg->checksum & 0xFF);
+	mavlink_ck_b(msg) = (uint8_t)(msg->checksum >> 8);
 
 	return length + MAVLINK_NUM_NON_PAYLOAD_BYTES;
 }
@@ -133,7 +133,7 @@ MAVLINK_HELPER void _mav_finalize_message_chan_send(mavlink_channel_t chan, uint
 	buf[4] = mavlink_system.compid;
 	buf[5] = msgid;
 	status->current_tx_seq++;
-	checksum = crc_calculate((uint8_t*)&buf[1], MAVLINK_CORE_HEADER_LEN);
+	checksum = crc_calculate((const uint8_t*)&buf[1], MAVLINK_CORE_HEADER_LEN);
 	crc_accumulate_buffer(&checksum, packet, length);
 #if MAVLINK_CRC_EXTRA
 	crc_accumulate(crc_extra, &checksum);
@@ -158,6 +158,7 @@ MAVLINK_HELPER void _mavlink_resend_uart(mavlink_channel_t chan, const mavlink_m
 
 	ck[0] = (uint8_t)(msg->checksum & 0xFF);
 	ck[1] = (uint8_t)(msg->checksum >> 8);
+	// XXX use the right sequence here
 
 	MAVLINK_START_UART_SEND(chan, MAVLINK_NUM_NON_PAYLOAD_BYTES + msg->len);
 	_mavlink_send_uart(chan, (const char *)&msg->magic, MAVLINK_NUM_HEADER_BYTES);
@@ -172,7 +173,13 @@ MAVLINK_HELPER void _mavlink_resend_uart(mavlink_channel_t chan, const mavlink_m
  */
 MAVLINK_HELPER uint16_t mavlink_msg_to_send_buffer(uint8_t *buffer, const mavlink_message_t *msg)
 {
-	memcpy(buffer, (const uint8_t *)&msg->magic, MAVLINK_NUM_NON_PAYLOAD_BYTES + (uint16_t)msg->len);
+	memcpy(buffer, (const uint8_t *)&msg->magic, MAVLINK_NUM_HEADER_BYTES + (uint16_t)msg->len);
+
+	uint8_t *ck = buffer + (MAVLINK_NUM_HEADER_BYTES + (uint16_t)msg->len);
+
+	ck[0] = (uint8_t)(msg->checksum & 0xFF);
+	ck[1] = (uint8_t)(msg->checksum >> 8);
+
 	return MAVLINK_NUM_NON_PAYLOAD_BYTES + (uint16_t)msg->len;
 }
 
diff --git a/mavlink/include/mavlink/v1.0/mavlink_types.h b/mavlink/include/mavlink/v1.0/mavlink_types.h
index 4019c619e0..43658e629e 100644
--- a/mavlink/include/mavlink/v1.0/mavlink_types.h
+++ b/mavlink/include/mavlink/v1.0/mavlink_types.h
@@ -28,6 +28,7 @@
 
 #define MAVLINK_MAX_EXTENDED_PAYLOAD_LEN (MAVLINK_MAX_EXTENDED_PACKET_LEN - MAVLINK_EXTENDED_HEADER_LEN - MAVLINK_NUM_NON_PAYLOAD_BYTES)
 
+#pragma pack(push, 1)
 typedef struct param_union {
 	union {
 		float param_float;
@@ -62,13 +63,12 @@ typedef struct __mavlink_message {
 	uint64_t payload64[(MAVLINK_MAX_PAYLOAD_LEN+MAVLINK_NUM_CHECKSUM_BYTES+7)/8];
 } mavlink_message_t;
 
-
 typedef struct __mavlink_extended_message {
        mavlink_message_t base_msg;
        int32_t extended_payload_len;   ///< Length of extended payload if any
        uint8_t extended_payload[MAVLINK_MAX_EXTENDED_PAYLOAD_LEN];
 } mavlink_extended_message_t;
-
+#pragma pack(pop)
 
 typedef enum {
 	MAVLINK_TYPE_CHAR     = 0,