diff --git a/man3/posix_spawn.3 b/man3/posix_spawn.3
index b9699345c..82aac67f3 100644
--- a/man3/posix_spawn.3
+++ b/man3/posix_spawn.3
@@ -394,6 +394,20 @@ instead of
 The
 .B _GNU_SOURCE
 feature test macro must be defined to obtain the definition of this contant.
+.TP
+.BR POSIX_SPAWN_SETSID " (since glibc 2.26)"
+If this flag is set,
+the child process shall create a new session and become the session leader.
+The child process shall also become the process group leader of the new process
+group in the session (see
+.BR setsid (2)).
+The
+.B _GNU_SOURCE
+feature test macro must be defined to obtain the definition of this contant.
+.\" This flag has been accepted in POSIX, see:
+.\" http://austingroupbugs.net/view.php?id=1044
+.\" and has been implemented in glibc since version 2.26
+.\" commit daeb1fa2e1b33323e719015f5f546988bd4cc73b
 .PP
 If
 .I attrp