diff --git a/convert_util.c b/convert_util.c
index 8ec725f..127c5a6 100644
--- a/convert_util.c
+++ b/convert_util.c
@@ -238,6 +238,23 @@ _convert_write_tlv_extended_tcp_hdr(uint8_t *buff, size_t buff_len,
 	return length;
 }
 
+static ssize_t
+_convert_write_tlv_cookie(uint8_t *buff, size_t buff_len,
+                          const struct convert_opts *opts)
+{
+	struct convert_cookie * cookie	= (struct convert_cookie *)buff;
+	size_t			length	= CONVERT_ALIGN(sizeof(*cookie) +
+	                                                opts->cookie_len);
+
+	if (buff_len < length)
+		return -1;
+
+	memset(cookie, '\0', length);
+	memcpy(cookie->opaque, opts->cookie_data, opts->cookie_len);
+
+	return length;
+}
+
 static struct {
 	uint32_t	flag;
 	uint8_t		type;
@@ -267,7 +284,7 @@ static struct {
 	[_CONVERT_F_COOKIE] =		 {
 		.flag	= CONVERT_F_COOKIE,
 		.type	= CONVERT_COOKIE,
-		.cb	= _convert_write_tlv_not_supp,
+		.cb	= _convert_write_tlv_cookie,
 	},
 	[_CONVERT_F_ERROR] =		 {
 		.flag	= CONVERT_F_ERROR,
diff --git a/tests/check_convert_util.c b/tests/check_convert_util.c
index 5f06840..0e69774 100644
--- a/tests/check_convert_util.c
+++ b/tests/check_convert_util.c
@@ -316,10 +316,11 @@ END_TEST
 
 START_TEST (test_convert_write_tlvs) {
 	unsigned int	i;
-	uint8_t *	(*tlv_builders[3])(size_t *len) = {
+	uint8_t *	(*tlv_builders[4])(size_t *len) = {
 		(uint8_t * (*)(size_t *))sample_convert_connect_tlv,
 		(uint8_t * (*)(size_t *))sample_convert_error_tlv,
-		(uint8_t * (*)(size_t *))sample_convert_tcp_ext_hdr_tlv
+		(uint8_t * (*)(size_t *))sample_convert_tcp_ext_hdr_tlv,
+		(uint8_t * (*)(size_t *))sample_convert_cookie_tlv,
 	};
 
 	/* For each TLV type, we expect convert_write(convert_read(TLV)) == TLV,