diff --git a/man2/sigaltstack.2 b/man2/sigaltstack.2
index ed47dbf55..6fccb4038 100644
--- a/man2/sigaltstack.2
+++ b/man2/sigaltstack.2
@@ -259,6 +259,22 @@ if (sigaltstack(&ss, NULL) == \-1)
     /* Handle error */;
 .fi
 .in
+.SH BUGS
+In the lead up to the development of the Linux 2.4 kernel,
+.\" Linux 2.3.40
+someone got confused and allowed the kernel to accept
+.B SS_ONSTACK
+in
+.IR ss.ss_flags ,
+which results behavior that is the same as when
+.I ss_flags
+is 0.
+On other implementations, and according to POSIX.1,
+.B SS_ONSTACK
+appears only as a reported flag in
+.IR old_ss.ss_flags .
+There is no need ever to specify this flag in
+.IR ss.ss_flags .
 .SH SEE ALSO
 .BR execve (2),
 .BR setrlimit (2),