diff --git a/programs/x509/cert_write.c b/programs/x509/cert_write.c
index be867ad..2dca1a1 100644
--- a/programs/x509/cert_write.c
+++ b/programs/x509/cert_write.c
@@ -447,7 +447,7 @@
     int key_idx = 0, offset = 0, ret = 0;
     const char * serial_port = NULL;
     unsigned char func_buffer[2];   /* Op code: 1 + key Id: 1 */
-    unsigned char pub_key_buf[65];  /* ECDSA Pub key: 64 + ASN.1 overhead: 1 */
+    unsigned char pub_key_buf[65];  /* ECDSA Pub key: 64 + EC octet string format tag: 1 */
     size_t rx_len = 0;
     static mbedtls_ecp_keypair ecp_key;