diff --git a/library/ssl_tls13_client.c b/library/ssl_tls13_client.c
index fa6c4c6..ae11364 100644
--- a/library/ssl_tls13_client.c
+++ b/library/ssl_tls13_client.c
@@ -1176,7 +1176,7 @@
         ssl->conf->early_data_enabled == MBEDTLS_SSL_EARLY_DATA_ENABLED) {
 
         ret = mbedtls_ssl_tls13_write_early_data_ext(
-            ssl, p, end, &ext_len, NULL);
+            ssl, 0, p, end, &ext_len);
         if (ret != 0) {
             return ret;
         }