diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index 960200f..3cdddf7 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -2255,6 +2255,10 @@
 /**
  * \brief          Set the random number generator callback
  *
+ * \note           The callback with its parameter must remain valid as
+ *                 long as there is an SSL context that uses the
+ *                 SSL configuration.
+ *
  * \param conf     SSL configuration
  * \param f_rng    RNG function (mandatory)
  * \param p_rng    RNG parameter