diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index 3a14a58..bf44975 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -493,10 +493,11 @@
  * \param buf      Buffer to write the received data to
  * \param len      Length of the receive buffer
  *
- * \return         The callback must return the number of bytes received,
- *                 or a non-zero error code.
- *                 If performing non-blocking I/O, \c MBEDTLS_ERR_SSL_WANT_READ
+ * \returns        If data has been received, the positive number of bytes received.
+ * \returns        \c 0 if the connection has been closed.
+ * \returns        If performing non-blocking I/O, \c MBEDTLS_ERR_SSL_WANT_READ
  *                 must be returned when the operation would block.
+ * \returns        Another negative error code on other kinds of failures.
  *
  * \note           The callback may receive fewer bytes than the length of the
  *                 buffer. It must always return the number of bytes actually