diff --git a/drivers/net/usb/hso.c b/drivers/net/usb/hso.c
index 86292e6aaf4955c4412ead6579f74e6848bcd089..1a482344b3f507e97486059d56280dfd3f23d37c 100644
--- a/drivers/net/usb/hso.c
+++ b/drivers/net/usb/hso.c
@@ -185,7 +185,6 @@ enum rx_ctrl_state{
 #define BM_REQUEST_TYPE (0xa1)
 #define B_NOTIFICATION  (0x20)
 #define W_VALUE         (0x0)
-#define W_INDEX         (0x2)
 #define W_LENGTH        (0x2)
 
 #define B_OVERRUN       (0x1<<6)
@@ -1487,6 +1486,7 @@ static void tiocmget_intr_callback(struct urb *urb)
 	struct uart_icount *icount;
 	struct hso_serial_state_notification *serial_state_notification;
 	struct usb_device *usb;
+	int if_num;
 
 	/* Sanity checks */
 	if (!serial)
@@ -1495,15 +1495,24 @@ static void tiocmget_intr_callback(struct urb *urb)
 		handle_usb_error(status, __func__, serial->parent);
 		return;
 	}
+
+	/* tiocmget is only supported on HSO_PORT_MODEM */
 	tiocmget = serial->tiocmget;
 	if (!tiocmget)
 		return;
+	BUG_ON((serial->parent->port_spec & HSO_PORT_MASK) != HSO_PORT_MODEM);
+
 	usb = serial->parent->usb;
+	if_num = serial->parent->interface->altsetting->desc.bInterfaceNumber;
+
+	/* wIndex should be the USB interface number of the port to which the
+	 * notification applies, which should always be the Modem port.
+	 */
 	serial_state_notification = &tiocmget->serial_state_notification;
 	if (serial_state_notification->bmRequestType != BM_REQUEST_TYPE ||
 	    serial_state_notification->bNotification != B_NOTIFICATION ||
 	    le16_to_cpu(serial_state_notification->wValue) != W_VALUE ||
-	    le16_to_cpu(serial_state_notification->wIndex) != W_INDEX ||
+	    le16_to_cpu(serial_state_notification->wIndex) != if_num ||
 	    le16_to_cpu(serial_state_notification->wLength) != W_LENGTH) {
 		dev_warn(&usb->dev,
 			 "hso received invalid serial state notification\n");