diff --git a/DownloadDCFirmware/mainwindow.cpp b/DownloadDCFirmware/mainwindow.cpp
index a9e1b8c..2639524 100644
--- a/DownloadDCFirmware/mainwindow.cpp
+++ b/DownloadDCFirmware/mainwindow.cpp
@@ -7,6 +7,11 @@
 #include <QScrollBar>
 #include <QEvent>
 
+#ifdef PTU5
+#define SERIAL_PORT "ttymxc2"
+#else
+#define SERIAL_PORT "ttyUSB0"
+#endif
 
 MainWindow::MainWindow(QWidget *parent)
     : QMainWindow(parent)
@@ -79,7 +84,7 @@ MainWindow::~MainWindow() {
 
 bool MainWindow::openSerialPort() {
    // const SettingsDialog::Settings p = m_settings->settings();
-   m_serial->setPortName("");
+   m_serial->setPortName(SERIAL_PORT);
    m_serial->setBaudRate(QSerialPort::Baud115200);
    m_serial->setDataBits(QSerialPort::DataBits::Data8);
    m_serial->setParity(QSerialPort::Parity::NoParity);