diff --git a/sys/compat/linux/linux_ioctl.c b/sys/compat/linux/linux_ioctl.c
--- a/sys/compat/linux/linux_ioctl.c
+++ b/sys/compat/linux/linux_ioctl.c
@@ -1009,8 +1009,12 @@
 		error = ENOIOCTL;
 		break;
 	case LINUX_TIOCSPTLCK:
-		/* Our unlockpt() does nothing. */
-		error = 0;
+		/*
+		 * Our unlockpt() does nothing. Check that fd refers
+		 * to a pseudo-terminal master device.
+		 */
+		args->cmd = TIOCPTMASTER;
+		error = (sys_ioctl(td, (struct ioctl_args *)args));
 		break;
 	default:
 		error = ENOIOCTL;