diff --git a/man4/tty_ioctl.4 b/man4/tty_ioctl.4
index e54be3cdb..ee279f818 100644
--- a/man4/tty_ioctl.4
+++ b/man4/tty_ioctl.4
@@ -361,6 +361,15 @@ locally \fB^S\fP/\fB^Q\fP flow-controlled remote login.
 Return the current packet mode setting in the integer pointed to by
 .IR argp 
 (since Linux 3.8).
+.TP
+.BI "TIOCSPTLCK	int *" argp
+Set (if
+.IR *argp
+is nonzero) or remove (if
+.IR *argp
+is zero) the pseudoterminal slave device.
+(See also
+.BR unlockpt (3).)
 .PP
 The BSD ioctls
 .BR TIOCSTOP ,