diff --git a/hw/usb/core.c b/hw/usb/core.c
index 87a513fa7e..632a8efe47 100644
--- a/hw/usb/core.c
+++ b/hw/usb/core.c
@@ -391,6 +391,7 @@ int usb_handle_packet(USBDevice *dev, USBPacket *p)
     if (QTAILQ_EMPTY(&p->ep->queue) || p->ep->pipeline) {
         ret = usb_process_one(p);
         if (ret == USB_RET_ASYNC) {
+            assert(p->ep->type != USB_ENDPOINT_XFER_ISOC);
             usb_packet_set_state(p, USB_PACKET_ASYNC);
             QTAILQ_INSERT_TAIL(&p->ep->queue, p, queue);
         } else if (ret == USB_RET_ADD_TO_QUEUE) {
diff --git a/hw/usb/hcd-ehci.c b/hw/usb/hcd-ehci.c
index 8ac78adf95..f14f9d7018 100644
--- a/hw/usb/hcd-ehci.c
+++ b/hw/usb/hcd-ehci.c
@@ -1667,7 +1667,6 @@ static int ehci_process_itd(EHCIState *ehci,
                                  (itd->transact[i] & ITD_XACT_IOC) != 0);
                 usb_packet_map(&ehci->ipacket, &ehci->isgl);
                 ret = usb_handle_packet(dev, &ehci->ipacket);
-                assert(ret != USB_RET_ASYNC);
                 usb_packet_unmap(&ehci->ipacket, &ehci->isgl);
             } else {
                 DPRINTF("ISOCH: attempt to addess non-iso endpoint\n");