diff --git a/man2/futex.2 b/man2/futex.2
index c80330f6e..3cc225241 100644
--- a/man2/futex.2
+++ b/man2/futex.2
@@ -874,6 +874,14 @@ via
 .BR FUTEX_WAKE
 without requeueing on
 .IR uaddr2 .
+
+The
+.I val3
+argument is ignored.
+.\" FIXME Re the preceding sentence, actually 'val3' is internally set to
+.\"       FUTEX_BITSET_MATCH_ANY before calling futex_wait_requeue_pi().
+.\"       I'm not sure we need to say anything about this though.
+.\"       Comments?
 .SH RETURN VALUE
 .PP
 In the event of an error, all operations return \-1 and set