diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index 1d392ab31..f563437d1 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -1392,18 +1392,25 @@ void mbedtls_ssl_set_bio( mbedtls_ssl_context *ssl,
  *                 example when a PMTU estimate becomes available from other
  *                 sources, such as lower (or higher) protocol layers.
  *
- * \note           This only controls the size of the packet we send.
+ * \note           This only controls the size of the packets we send.
  *                 Client-side, you can request the server to use smaller
  *                 records with \c mbedtls_ssl_conf_max_frag_len().
  *
  * \note           If both a MTU and a maximum fragment length have been
- *                 configured (or negotiated with the peer), the lower limit
- *                 is used.
+ *                 configured (or negotiated with the peer), the resulting
+ *                 lower limit (after translating the MTU setting to a limit
+ *                 on the record content length) is used.
  *
- * \note           Values larger than #MBEDTLS_SSL_OUT_CONTENT_LEN have no
- *                 effect. This can only be used to decrease the maximum size
- *                 of datagrams sent. Values lower than record layer expansion
- *                 are ignored.
+ * \note           This can only be used to decrease the maximum size
+ *                 of datagrams sent. It cannot be used to increase the
+ *                 maximum size of records over the limit set by
+ *                 #MBEDTLS_SSL_OUT_CONTENT_LEN.
+ *
+ * \note           Values lower than the current record layer expansion will
+ *                 result in an error when trying to send data.
+ *
+ * \note           Using record compression together with a non-zero MTU value
+ *                 will result in an error when trying to send data.
  *
  * \param ssl      SSL context
  * \param mtu      Value of the path MTU in bytes