diff --git a/drivers/input/serio/serport.c b/drivers/input/serio/serport.c
index 8755f5f3ad37c2218de60b96782c0863615a705e..0cb7ef59071b792a350a914e88f4e9be7da34efc 100644
--- a/drivers/input/serio/serport.c
+++ b/drivers/input/serio/serport.c
@@ -124,7 +124,7 @@ static void serport_ldisc_receive(struct tty_struct *tty, const unsigned char *c
 {
 	struct serport *serport = (struct serport*) tty->disc_data;
 	unsigned long flags;
-	unsigned int ch_flags;
+	unsigned int ch_flags = 0;
 	int i;
 
 	spin_lock_irqsave(&serport->lock, flags);
@@ -133,18 +133,20 @@ static void serport_ldisc_receive(struct tty_struct *tty, const unsigned char *c
 		goto out;
 
 	for (i = 0; i < count; i++) {
-		switch (fp[i]) {
-		case TTY_FRAME:
-			ch_flags = SERIO_FRAME;
-			break;
-
-		case TTY_PARITY:
-			ch_flags = SERIO_PARITY;
-			break;
-
-		default:
-			ch_flags = 0;
-			break;
+		if (fp) {
+			switch (fp[i]) {
+			case TTY_FRAME:
+				ch_flags = SERIO_FRAME;
+				break;
+
+			case TTY_PARITY:
+				ch_flags = SERIO_PARITY;
+				break;
+
+			default:
+				ch_flags = 0;
+				break;
+			}
 		}
 
 		serio_interrupt(serport->serio, cp[i], ch_flags);
diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index c0f76da553042db2f3eadb91cfb9ff08bc60e43d..c09db11b8831d8b9f5b8b05413e0907a46ba1299 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2269,14 +2269,15 @@ static void gsmld_receive_buf(struct tty_struct *tty, const unsigned char *cp,
 	char *f;
 	int i;
 	char buf[64];
-	char flags;
+	char flags = TTY_NORMAL;
 
 	if (debug & 4)
 		print_hex_dump_bytes("gsmld_receive: ", DUMP_PREFIX_OFFSET,
 				     cp, count);
 
 	for (i = count, dp = cp, f = fp; i; i--, dp++) {
-		flags = *f++;
+		if (f)
+			flags = *f++;
 		switch (flags) {
 		case TTY_NORMAL:
 			gsm->receive(gsm, *dp);
diff --git a/drivers/tty/n_r3964.c b/drivers/tty/n_r3964.c
index 1e6405070ce649e356b24d272a824e9eda737159..8b157d68a03e97aa2089d9b3c4d98fdb0b109719 100644
--- a/drivers/tty/n_r3964.c
+++ b/drivers/tty/n_r3964.c
@@ -1244,7 +1244,7 @@ static void r3964_receive_buf(struct tty_struct *tty, const unsigned char *cp,
 {
 	struct r3964_info *pInfo = tty->disc_data;
 	const unsigned char *p;
-	char *f, flags = 0;
+	char *f, flags = TTY_NORMAL;
 	int i;
 
 	for (i = count, p = cp, f = fp; i; i--, p++) {
diff --git a/include/linux/tty_ldisc.h b/include/linux/tty_ldisc.h
index f15c898ff462006fb0bec91d5922ecbf24267d8c..b8347c207cb845d940ed163cb89776e0bacaf252 100644
--- a/include/linux/tty_ldisc.h
+++ b/include/linux/tty_ldisc.h
@@ -84,7 +84,8 @@
  *	processing.  <cp> is a pointer to the buffer of input
  *	character received by the device.  <fp> is a pointer to a
  *	pointer of flag bytes which indicate whether a character was
- *	received with a parity error, etc.
+ *	received with a parity error, etc. <fp> may be NULL to indicate
+ *	all data received is TTY_NORMAL.
  *
  * void	(*write_wakeup)(struct tty_struct *);
  *
@@ -118,7 +119,8 @@
  *	processing.  <cp> is a pointer to the buffer of input
  *	character received by the device.  <fp> is a pointer to a
  *	pointer of flag bytes which indicate whether a character was
- *	received with a parity error, etc.
+ *	received with a parity error, etc. <fp> may be NULL to indicate
+ *	all data received is TTY_NORMAL.
  *	If assigned, prefer this function for automatic flow control.
  */