diff --git a/drivers/char/pty.c b/drivers/char/pty.c
index 9d1b4f5..6e6942c 100644
--- a/drivers/char/pty.c
+++ b/drivers/char/pty.c
@@ -22,6 +22,7 @@
 #include <linux/major.h>
 #include <linux/mm.h>
 #include <linux/init.h>
+#include <linux/smp_lock.h>
 #include <linux/sysctl.h>
 #include <linux/device.h>
 #include <linux/uaccess.h>