diff --git a/portcontrol.cpp b/portcontrol.cpp
--- a/portcontrol.cpp
+++ b/portcontrol.cpp
@@ -42,6 +42,10 @@ PortControl::PortControl(QSerialPort* po
                      SELECT<const QString&>::OVERLOAD_OF(&QComboBox::activated),
                      this, &PortControl::selectPort);
 
+    QObject::connect(ui->cbPortList,
+                     SELECT<const QString&>::OVERLOAD_OF(&QComboBox::activated),
+                     this, &PortControl::onPortNameChanged);
+
     QObject::connect(ui->cbBaudRate,
                      SELECT<const QString&>::OVERLOAD_OF(&QComboBox::activated),
                      this, &PortControl::selectBaudRate);
@@ -105,11 +109,15 @@ void PortControl::loadPortList()
 
     ui->cbPortList->clear();
 
+    discoveredPorts.clear();
     for (auto port : QSerialPortInfo::availablePorts())
     {
         ui->cbPortList->addItem(port.portName());
+        discoveredPorts << port.portName();
     }
 
+    ui->cbPortList->addItems(userEnteredPorts);
+
     // find current selection in the new list, maybe it doesn't exist anymore?
     int currentSelectionIndex = ui->cbPortList->findText(currentSelection);
     if (currentSelectionIndex >= 0)
@@ -245,3 +253,13 @@ void PortControl::enableSkipByte(bool en
 {
     ui->pbSkipByte->setDisabled(enabled);
 }
+
+void PortControl::onPortNameChanged(QString portName)
+{
+    // was this a user entered name?
+    if(!discoveredPorts.contains(portName) &&
+       !userEnteredPorts.contains(portName))
+    {
+        userEnteredPorts << portName;
+    }
+}
diff --git a/portcontrol.h b/portcontrol.h
--- a/portcontrol.h
+++ b/portcontrol.h
@@ -23,6 +23,7 @@
 #include <QWidget>
 #include <QButtonGroup>
 #include <QSerialPort>
+#include <QStringList>
 
 namespace Ui {
 class PortControl;
@@ -46,6 +47,9 @@ private:
     QButtonGroup stopBitsButtons;
     QButtonGroup flowControlButtons;
 
+    QStringList discoveredPorts; // list of port names returned by availablePorts
+    QStringList userEnteredPorts; // list of port names entered by user
+
 public slots:
     void loadPortList();
     void loadBaudRateList();
@@ -59,6 +63,9 @@ public slots:
     void selectStopBits(int stopBits); // stopBits must be one of QSerialPort::StopBits
     void selectFlowControl(int flowControl); // flowControl must be one of QSerialPort::FlowControl
 
+private slots:
+    void onPortNameChanged(QString portName);
+
 signals:
     void skipByteRequested();
     void portToggled(bool open);