diff --git a/man2/ioctl_tty.2 b/man2/ioctl_tty.2
index ac46725d2..186011ee7 100644
--- a/man2/ioctl_tty.2
+++ b/man2/ioctl_tty.2
@@ -386,6 +386,9 @@ Set the foreground process group ID of this terminal.
 Argument:
 .BI "pid_t *" argp
 .IP
+When successful, equivalent to
+.IR "*argp = tcgetsid(fd)" .
+.IP
 Get the session ID of the given terminal.
 This fails with the error
 .B ENOTTY