diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index 60f59a9..6084a51 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -1579,14 +1579,24 @@
 
 #if defined(MBEDTLS_X509_CRT_PARSE_C)
 /**
- * \brief          Set hostname for ServerName TLS extension
- *                 (client-side only)
+ * \brief          Set or reset the hostname to check against the received 
+ *                 server certificate. It sets the ServerName TLS extension, 
+ *                 too, if that extension is enabled. (client-side only)
  *
  *
  * \param ssl      SSL context
- * \param hostname the server hostname
+ * \param hostname the server hostname, may be NULL to clear hostname
+ 
+ * \note           Maximum hostname length MBEDTLS_SSL_MAX_HOST_NAME_LEN.
  *
- * \return         0 if successful or MBEDTLS_ERR_SSL_ALLOC_FAILED
+ * \return         0 if successful, MBEDTLS_ERR_SSL_ALLOC_FAILED on 
+ *                 allocation failure, MBEDTLS_ERR_BAD_INPUT_DATA on 
+ *                 too long input hostname.
+ *
+ * \post           Hostname set to the one provided on success (cleared
+ *                 when NULL). On allocation failure hostname is cleared. 
+ *                 On too long input failure, old hostname is unchanged.
+ *
  */
 int mbedtls_ssl_set_hostname( mbedtls_ssl_context *ssl, const char *hostname );
 #endif /* MBEDTLS_X509_CRT_PARSE_C */