diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index b2f5c67..8c44287 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -1535,7 +1535,7 @@
  * \brief          Set the random number generator callback
  *
  * \param conf     SSL configuration
- * \param f_rng    RNG function
+ * \param f_rng    RNG function (mandatory)
  * \param p_rng    RNG parameter
  */
 void mbedtls_ssl_conf_rng( mbedtls_ssl_config *conf,
diff --git a/include/mbedtls/ssl_ticket.h b/include/mbedtls/ssl_ticket.h
index 871eec3..1047dbb 100644
--- a/include/mbedtls/ssl_ticket.h
+++ b/include/mbedtls/ssl_ticket.h
@@ -90,7 +90,7 @@
  * \brief           Prepare context to be actually used
  *
  * \param ctx       Context to be set up
- * \param f_rng     RNG callback function
+ * \param f_rng     RNG callback function (mandatory)
  * \param p_rng     RNG callback context
  * \param cipher    AEAD cipher to use for ticket protection.
  *                  Recommended value: MBEDTLS_CIPHER_AES_256_GCM.