diff --git a/drivers/net/usb/cdc_ncm.c b/drivers/net/usb/cdc_ncm.c
index 2fb31edab125..53759c315b97 100644
--- a/drivers/net/usb/cdc_ncm.c
+++ b/drivers/net/usb/cdc_ncm.c
@@ -740,12 +740,14 @@ static void cdc_ncm_free(struct cdc_ncm_ctx *ctx)
 int cdc_ncm_change_mtu(struct net_device *net, int new_mtu)
 {
 	struct usbnet *dev = netdev_priv(net);
-	struct cdc_ncm_ctx *ctx = (struct cdc_ncm_ctx *)dev->data[0];
-	int maxmtu = ctx->max_datagram_size - cdc_ncm_eth_hlen(dev);
+	int maxmtu = cdc_ncm_max_dgram_size(dev) - cdc_ncm_eth_hlen(dev);
 
 	if (new_mtu <= 0 || new_mtu > maxmtu)
 		return -EINVAL;
+
 	net->mtu = new_mtu;
+	cdc_ncm_set_dgram_size(dev, new_mtu + cdc_ncm_eth_hlen(dev));
+
 	return 0;
 }
 EXPORT_SYMBOL_GPL(cdc_ncm_change_mtu);