diff --git a/man7/unix.7 b/man7/unix.7
index c08218702..cbc0b314d 100644
--- a/man7/unix.7
+++ b/man7/unix.7
@@ -436,6 +436,10 @@ message, the
 .B SO_PASSCRED
 option must be enabled on the socket.
 .PP
+When sending ancillary data with
+.BR sendmsg (2),
+only one item of each of the above types may be included in the sent message.
+.PP
 If the space allocated for receiving incoming ancillary data is too small,
 then the ancillary data is truncated to the number of headers
 that will fit in the supplied buffer (or, in the case of an