diff --git a/drivers/usb/gadget/function/f_cdev.c b/drivers/usb/gadget/function/f_cdev.c
index 31ec75fed944..0e300b12979e 100644
--- a/drivers/usb/gadget/function/f_cdev.c
+++ b/drivers/usb/gadget/function/f_cdev.c
@@ -1556,8 +1556,10 @@ int usb_cser_connect(struct f_cdev *port)
 
 void usb_cser_disconnect(struct f_cdev *port)
 {
+	struct cserial *cser;
 	unsigned long flags;
 
+	cser = &port->port_usb;
 	usb_cser_stop_io(port);
 
 	/* lower DTR to modem */
@@ -1565,6 +1567,7 @@ void usb_cser_disconnect(struct f_cdev *port)
 
 	spin_lock_irqsave(&port->port_lock, flags);
 	port->is_connected = false;
+	cser->notify_modem = NULL;
 	port->nbytes_from_host = port->nbytes_to_host = 0;
 	port->nbytes_to_port_bridge = 0;
 	spin_unlock_irqrestore(&port->port_lock, flags);