diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index 39c7db7bcd21..c70f34993623 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -416,7 +416,7 @@ static void acm_ctrl_irq(struct urb *urb)
 	expected_size = sizeof(struct usb_cdc_notification) +
 					le16_to_cpu(dr->wLength);
 
-	if (current_size < expected_size) {
+	if (acm->nb_index != 0 || current_size < expected_size) {
 		/* notification is transmitted fragmented, reassemble */
 		if (acm->nb_size < expected_size) {
 			u8 *new_buffer;