diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index 9fd1cd99aa97..13df3c8cd7bf 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -844,6 +844,7 @@ static int set_serial_info(struct acm *acm,
 {
 	struct serial_struct new_serial;
 	unsigned int closing_wait, close_delay;
+	unsigned int old_closing_wait, old_close_delay;
 	int retval = 0;
 
 	if (copy_from_user(&new_serial, newinfo, sizeof(new_serial)))
@@ -854,18 +855,24 @@ static int set_serial_info(struct acm *acm,
 			ASYNC_CLOSING_WAIT_NONE :
 			msecs_to_jiffies(new_serial.closing_wait * 10);
 
+	/* we must redo the rounding here, so that the values match */
+	old_close_delay	= jiffies_to_msecs(acm->port.close_delay) / 10;
+	old_closing_wait = acm->port.closing_wait == ASYNC_CLOSING_WAIT_NONE ?
+				ASYNC_CLOSING_WAIT_NONE :
+				jiffies_to_msecs(acm->port.closing_wait) / 10;
+
 	mutex_lock(&acm->port.mutex);
 
-	if (!capable(CAP_SYS_ADMIN)) {
-		if ((close_delay != acm->port.close_delay) ||
-		    (closing_wait != acm->port.closing_wait))
+	if ((new_serial.close_delay != old_close_delay) ||
+            (new_serial.closing_wait != old_closing_wait)) {
+		if (!capable(CAP_SYS_ADMIN))
 			retval = -EPERM;
-		else
-			retval = -EOPNOTSUPP;
-	} else {
-		acm->port.close_delay  = close_delay;
-		acm->port.closing_wait = closing_wait;
-	}
+		else {
+			acm->port.close_delay  = close_delay;
+			acm->port.closing_wait = closing_wait;
+		}
+	} else
+		retval = -EOPNOTSUPP;
 
 	mutex_unlock(&acm->port.mutex);
 	return retval;