diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index 5f1bf79..5164460 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -2229,7 +2229,9 @@
  *
  * \note           When this function returns MBEDTLS_ERR_SSL_WANT_WRITE/READ,
  *                 it must be called later with the *same* arguments,
- *                 until it returns a positive value.
+ *                 until it returns a positive value. When the function returns
+ *                 MBEDTLS_ERR_SSL_WANT_WRITE there may be some partial
+ *                 data in the output buffer, however this is not yet sent.
  *
  * \note           If the requested length is greater than the maximum
  *                 fragment length (either the built-in limit or the one set