diff --git a/include/mbedtls/net_sockets.h b/include/mbedtls/net_sockets.h
index 55fd18b..310b397 100644
--- a/include/mbedtls/net_sockets.h
+++ b/include/mbedtls/net_sockets.h
@@ -155,6 +155,10 @@
 /**
  * \brief          Check and wait for the context to be ready for read/write
  *
+ * \note           The current implementation of this function uses
+ *                 select() and returns an error if the file descriptor
+ *                 is beyond \c FD_SETSIZE.
+ *
  * \param ctx      Socket to check
  * \param rw       Bitflag composed of MBEDTLS_NET_POLL_READ and
  *                 MBEDTLS_NET_POLL_WRITE specifying the events
@@ -236,6 +240,10 @@
  *                 'timeout' seconds. If no error occurs, the actual amount
  *                 read is returned.
  *
+ * \note           The current implementation of this function uses
+ *                 select() and returns an error if the file descriptor
+ *                 is beyond \c FD_SETSIZE.
+ *
  * \param ctx      Socket
  * \param buf      The buffer to write to
  * \param len      Maximum length of the buffer