diff --git a/include/mbedtls/net_sockets.h b/include/mbedtls/net_sockets.h
index 0d61547..67fe1e9 100644
--- a/include/mbedtls/net_sockets.h
+++ b/include/mbedtls/net_sockets.h
@@ -219,6 +219,10 @@
  *                 '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