diff --git a/ctap.c b/ctap.c
index ab78ef2..d780673 100644
--- a/ctap.c
+++ b/ctap.c
@@ -763,7 +763,7 @@ void ctap_make_credential(CborEncoder * encoder, uint8_t * request, int length)
 
     printf("der sig [%d]: ", sigder_sz); dump_hex(sigder, sigder_sz);
 
-    ctap_add_attest_statement(&map, sigder, sigderlen);
+    ctap_add_attest_statement(&map, sigder, sigder_sz);
 
     ret = cbor_encoder_close_container(encoder, &map);
     check_ret(ret);
diff --git a/ctaphid.c b/ctaphid.c
index aa0bb00..2999653 100644
--- a/ctaphid.c
+++ b/ctaphid.c
@@ -185,7 +185,7 @@ static int buffer_len()
 static void ctaphid_write(CTAPHID_WRITE_BUFFER * wb, void * _data, int len)
 {
     uint8_t * data = (uint8_t *)_data;
-    if (len == 0)
+    if (_data == NULL)
     {
         if (wb->offset == 0 && wb->bytes_written == 0)
         {