diff --git a/sys/dev/usb/serial/umodem.c b/sys/dev/usb/serial/umodem.c
--- a/sys/dev/usb/serial/umodem.c
+++ b/sys/dev/usb/serial/umodem.c
@@ -218,6 +218,7 @@
 		    uint8_t *);
 static int	umodem_pre_param(struct ucom_softc *, struct termios *);
 static void	umodem_cfg_param(struct ucom_softc *, struct termios *);
+static void	umodem_cfg_open(struct ucom_softc *ucom);
 static int	umodem_ioctl(struct ucom_softc *, uint32_t, caddr_t, int,
 		    struct thread *);
 static void	umodem_cfg_set_dtr(struct ucom_softc *, uint8_t);
@@ -283,6 +284,7 @@
 	.ucom_cfg_set_break = &umodem_cfg_set_break,
 	.ucom_cfg_param = &umodem_cfg_param,
 	.ucom_pre_param = &umodem_pre_param,
+	.ucom_cfg_open = &umodem_cfg_open,
 	.ucom_ioctl = &umodem_ioctl,
 	.ucom_start_read = &umodem_start_read,
 	.ucom_stop_read = &umodem_stop_read,
@@ -633,6 +635,17 @@
 	    &req, &ls, 0, 1000);
 }
 
+static void	
+umodem_cfg_open(struct ucom_softc *ucom)
+{
+	struct umodem_softc *sc = ucom->sc_parent;
+
+	if ((sc->sc_super_ucom.sc_flag & UCOM_FLAG_DEVICE_MODE) == 0) {
+		usbd_xfer_set_stall(sc->sc_xfer[UMODEM_BULK_WR]);
+		usbd_xfer_set_stall(sc->sc_xfer[UMODEM_BULK_RD]);
+	}
+}
+
 static int
 umodem_ioctl(struct ucom_softc *ucom, uint32_t cmd, caddr_t data,
     int flag, struct thread *td)
diff --git a/sys/dev/usb/serial/usb_serial.c b/sys/dev/usb/serial/usb_serial.c
--- a/sys/dev/usb/serial/usb_serial.c
+++ b/sys/dev/usb/serial/usb_serial.c
@@ -628,9 +628,9 @@
 		task->termios_copy = *pt;
 
 	/*
-	 * Closing the device should be synchronous.
+	 * Closing or opening the device should be synchronous.
 	 */
-	if (fn == ucom_cfg_close)
+	if (fn == ucom_cfg_close || fn == ucom_cfg_open)
 		usb_proc_mwait(&ssc->sc_tq, t0, t1);
 
 	/*