--- x/drivers/tty/serial/serial_port.c
+++ y/drivers/tty/serial/serial_port.c
@@ -37,7 +37,8 @@ static int serial_port_runtime_resume(st
 	/* Flush any pending TX for the port */
 	spin_lock_irqsave(&port->lock, flags);
 	if (__serial_port_busy(port))
-		port->ops->start_tx(port);
+		if (port->ops && port->ops->start_tx)
+			port->ops->start_tx(port);
 	spin_unlock_irqrestore(&port->lock, flags);
 
 out: