diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index a4d0dde..a2b4cdd 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -4088,6 +4088,10 @@
  * \brief          Return the (D)TLS protocol version negotiated in the
  *                 given connection.
  *
+ * \note           If you call this function too early during the initial
+ *                 handshake, before the two sides have agreed on a version,
+ *                 this function returns #MBEDTLS_SSL_VERSION_UNKNOWN.
+ *
  * \param ssl      The SSL context to query.
  * \return         The negotiated protocol version.
  */