2 files changed, 13 insertions, 0 deletions
diff --git a/src/serialbus/qmodbusdevice.cpp b/src/serialbus/qmodbusdevice.cpp
index 4aaae87..7ef358c 100644
--- a/src/serialbus/qmodbusdevice.cpp
+++ b/src/serialbus/qmodbusdevice.cpp
@@ -258,6 +258,9 @@ bool QModbusDevice::connectDevice()
 */
 void QModbusDevice::disconnectDevice()
 {
+    if (state() == QModbusDevice::UnconnectedState)
+        return;
+
     setState(QModbusDevice::ClosingState);
 
     //Unconnected is set by backend -> might be delayed by event loop
diff --git a/tests/auto/qmodbusdevice/tst_qmodbusdevice.cpp b/tests/auto/qmodbusdevice/tst_qmodbusdevice.cpp
index 836d881..748c4bf 100644
--- a/tests/auto/qmodbusdevice/tst_qmodbusdevice.cpp
+++ b/tests/auto/qmodbusdevice/tst_qmodbusdevice.cpp
@@ -64,6 +64,7 @@ private slots:
     void cleanupTestCase();
 
     void connectDevice();
+    void disconnectDevice();
     void state();
     void error();
 
@@ -98,6 +99,15 @@ void tst_QModbusDevice::connectDevice()
     QVERIFY(!device->connectDevice());
 }
 
+void tst_QModbusDevice::disconnectDevice()
+{
+    //see QTBUG-66648
+    DummyDevice dev;
+    QCOMPARE(dev.state(), QModbusDevice::UnconnectedState);
+    dev.disconnectDevice();
+    QCOMPARE(dev.state(), QModbusDevice::UnconnectedState);
+}
+
 void tst_QModbusDevice::state()
 {
     device->setState(QModbusDevice::ConnectedState);