diff --git a/src/modules/mavlink/mavlink_ftp.cpp b/src/modules/mavlink/mavlink_ftp.cpp
index 72ede87976..ae9246ece0 100644
--- a/src/modules/mavlink/mavlink_ftp.cpp
+++ b/src/modules/mavlink/mavlink_ftp.cpp
@@ -224,12 +224,14 @@ MavlinkFTP::_process_request(Request *req)
 out:
 	// handle success vs. error
 	if (errorCode == kErrNone) {
+		payload->req_opcode = payload->opcode;
 		payload->opcode = kRspAck;
 #ifdef MAVLINK_FTP_DEBUG
 		warnx("FTP: ack\n");
 #endif
 	} else {
 		warnx("FTP: nak %u", errorCode);
+		payload->req_opcode = payload->opcode;
 		payload->opcode = kRspNak;
 		payload->size = 1;
 		payload->data[0] = errorCode;
@@ -654,7 +656,6 @@ MavlinkFTP::_payload_crc32(PayloadHeader *payload)
 	payload->crc32 = 0;
 	payload->padding[0] = 0;
 	payload->padding[1] = 0;
-	payload->padding[2] = 0;
 	uint32_t retCRC = crc32((const uint8_t*)payload, payload->size + sizeof(PayloadHeader));
 	payload->crc32 = saveCRC;
 		
diff --git a/src/modules/mavlink/mavlink_ftp.h b/src/modules/mavlink/mavlink_ftp.h
index b4cc154d11..1fb50a17e6 100644
--- a/src/modules/mavlink/mavlink_ftp.h
+++ b/src/modules/mavlink/mavlink_ftp.h
@@ -76,7 +76,8 @@ public:
 		uint8_t		session;	///< Session id for read and write commands
 		uint8_t		opcode;		///< Command opcode
 		uint8_t		size;		///< Size of data
-		uint8_t		padding[3];	///< 32 bit aligment padding
+		uint8_t		req_opcode;	///< Request opcode returned in kRspAck, kRspNak message
+		uint8_t		padding[2];	///< 32 bit aligment padding
 		uint32_t	crc32;		///< CRC for entire Request structure, with crc32 and padding set to 0
 		uint32_t	offset;		///< Offsets for List and Read commands
 		uint8_t		data[];		///< command data, varies by Opcode