diff --git a/contrib/libfido2/src/iso7816.c b/contrib/libfido2/src/iso7816.c
index a11aae3e99d1..a4902277c6d8 100644
--- a/contrib/libfido2/src/iso7816.c
+++ b/contrib/libfido2/src/iso7816.c
@@ -1,64 +1,64 @@
 /*
  * Copyright (c) 2018 Yubico AB. All rights reserved.
  * Use of this source code is governed by a BSD-style
  * license that can be found in the LICENSE file.
  */
 
 #include "fido.h"
 
 iso7816_apdu_t *
 iso7816_new(uint8_t cla, uint8_t ins, uint8_t p1, uint16_t payload_len)
 {
 	iso7816_apdu_t *apdu;
 	size_t alloc_len;
 
 	alloc_len = sizeof(iso7816_apdu_t) + payload_len + 2; /* le1 le2 */
 	if ((apdu = calloc(1, alloc_len)) == NULL)
 		return NULL;
 	apdu->alloc_len = alloc_len;
 	apdu->payload_len = payload_len;
 	apdu->payload_ptr = apdu->payload;
 	apdu->header.cla = cla;
 	apdu->header.ins = ins;
 	apdu->header.p1 = p1;
 	apdu->header.lc2 = (uint8_t)((payload_len >> 8) & 0xff);
 	apdu->header.lc3 = (uint8_t)(payload_len & 0xff);
 
 	return apdu;
 }
 
 void
 iso7816_free(iso7816_apdu_t **apdu_p)
 {
 	iso7816_apdu_t *apdu;
 
 	if (apdu_p == NULL || (apdu = *apdu_p) == NULL)
 		return;
 	freezero(apdu, apdu->alloc_len);
 	*apdu_p = NULL;
 }
 
 int
 iso7816_add(iso7816_apdu_t *apdu, const void *buf, size_t cnt)
 {
 	if (cnt > apdu->payload_len || cnt > UINT16_MAX)
 		return -1;
 	memcpy(apdu->payload_ptr, buf, cnt);
 	apdu->payload_ptr += cnt;
 	apdu->payload_len = (uint16_t)(apdu->payload_len - cnt);
 
 	return 0;
 }
 
 const unsigned char *
 iso7816_ptr(const iso7816_apdu_t *apdu)
 {
 	return (const unsigned char *)&apdu->header;
 }
 
 size_t
 iso7816_len(const iso7816_apdu_t *apdu)
 {
-	return apdu->alloc_len - sizeof(apdu->alloc_len) -
-	    sizeof(apdu->payload_len) - sizeof(apdu->payload_ptr);
+	return apdu->alloc_len - offsetof(iso7816_apdu_t, header) -
+	    (sizeof(iso7816_apdu_t) - offsetof(iso7816_apdu_t, payload));
 }
diff --git a/contrib/libfido2/src/iso7816.h b/contrib/libfido2/src/iso7816.h
index 5f5363a63a56..9bfad1fbab9d 100644
--- a/contrib/libfido2/src/iso7816.h
+++ b/contrib/libfido2/src/iso7816.h
@@ -1,49 +1,48 @@
 /*
  * Copyright (c) 2018 Yubico AB. All rights reserved.
  * Use of this source code is governed by a BSD-style
  * license that can be found in the LICENSE file.
  */
 
 #ifndef _ISO7816_H
 #define _ISO7816_H
 
 #include <stdint.h>
 #include <stdlib.h>
 
 #include "packed.h"
 
 #ifdef __cplusplus
 extern "C" {
 #endif /* __cplusplus */
 
 PACKED_TYPE(iso7816_header_t,
 struct iso7816_header {
 	uint8_t cla;
 	uint8_t ins;
 	uint8_t p1;
 	uint8_t p2;
 	uint8_t lc1;
 	uint8_t lc2;
 	uint8_t lc3;
 })
 
-PACKED_TYPE(iso7816_apdu_t,
-struct iso7816_apdu {
+typedef struct iso7816_apdu {
 	size_t            alloc_len;
 	uint16_t          payload_len;
 	uint8_t          *payload_ptr;
 	iso7816_header_t  header;
 	uint8_t           payload[];
-})
+} iso7816_apdu_t;
 
 const unsigned char *iso7816_ptr(const iso7816_apdu_t *);
 int iso7816_add(iso7816_apdu_t *, const void *, size_t);
 iso7816_apdu_t *iso7816_new(uint8_t, uint8_t, uint8_t, uint16_t);
 size_t iso7816_len(const iso7816_apdu_t *);
 void iso7816_free(iso7816_apdu_t **);
 
 #ifdef __cplusplus
 } /* extern "C" */
 #endif /* __cplusplus */
 
 #endif /* !_ISO7816_H */