diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index 4d3c701..98b65a2 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -1180,7 +1180,7 @@
 		if (*str == ',')
 			str++;
 		if (*str == '\0')
-			str = 0;
+			str = NULL;
 
 		if (tty_line >= 0 && tty_line <= p->num && p->poll_init &&
 				!p->poll_init(p, tty_line, str)) {