diff --git a/sys/dev/usb/ehci.c b/sys/dev/usb/ehci.c
index 2cd5bc5c534..d15ccb4ab0b 100644
--- a/sys/dev/usb/ehci.c
+++ b/sys/dev/usb/ehci.c
@@ -661,9 +661,13 @@ ehci_pcd_enable(void *v_sc)
 static __inline void
 hacksync(usbd_xfer_handle xfer)
 {
-	usbd_pipe_handle pipe = xfer->pipe;
-	bus_dma_tag_t tag = pipe->device->bus->buffer_dmatag;
-	struct usb_dma_mapping *dmap = &xfer->dmamap;
+	bus_dma_tag_t tag;
+	struct usb_dma_mapping *dmap;
+
+	if (xfer->length == 0)
+		return;
+	tag = xfer->pipe->device->bus->buffer_dmatag;
+	dmap = &xfer->dmamap;
 	bus_dmamap_sync(tag, dmap->map, BUS_DMASYNC_PREWRITE);
 }
 
diff --git a/sys/dev/usb/ohci.c b/sys/dev/usb/ohci.c
index 3b953025f91..7afc0c2ed4c 100644
--- a/sys/dev/usb/ohci.c
+++ b/sys/dev/usb/ohci.c
@@ -1568,9 +1568,13 @@ ohci_device_bulk_done(usbd_xfer_handle xfer)
 static __inline void
 hacksync(usbd_xfer_handle xfer)
 {
-	usbd_pipe_handle pipe = xfer->pipe;
-	bus_dma_tag_t tag = pipe->device->bus->buffer_dmatag;
-	struct usb_dma_mapping *dmap = &xfer->dmamap;
+	bus_dma_tag_t tag;
+	struct usb_dma_mapping *dmap;
+
+	if (xfer->length == 0)
+		return;
+	tag = xfer->pipe->device->bus->buffer_dmatag;
+	dmap = &xfer->dmamap;
 	bus_dmamap_sync(tag, dmap->map, BUS_DMASYNC_PREWRITE);
 }