diff --git a/src/widgets/widgets/qcombobox.cpp b/src/widgets/widgets/qcombobox.cpp
index a83aecf52c..b38b482295 100644
--- a/src/widgets/widgets/qcombobox.cpp
+++ b/src/widgets/widgets/qcombobox.cpp
@@ -1986,6 +1986,8 @@ void QComboBox::setModel(QAbstractItemModel *model)
                 this, SLOT(_q_emitHighlighted(QModelIndex)), Qt::UniqueConnection);
     }
 
+    setRootModelIndex(QModelIndex());
+
     bool currentReset = false;
 
     if (count()) {
@@ -2024,6 +2026,8 @@ QModelIndex QComboBox::rootModelIndex() const
 void QComboBox::setRootModelIndex(const QModelIndex &index)
 {
     Q_D(QComboBox);
+    if (d->root == index)
+        return;
     d->root = QPersistentModelIndex(index);
     view()->setRootIndex(index);
     update();
diff --git a/tests/auto/widgets/widgets/qcombobox/tst_qcombobox.cpp b/tests/auto/widgets/widgets/qcombobox/tst_qcombobox.cpp
index 556602b523..5007983aa6 100644
--- a/tests/auto/widgets/widgets/qcombobox/tst_qcombobox.cpp
+++ b/tests/auto/widgets/widgets/qcombobox/tst_qcombobox.cpp
@@ -1577,11 +1577,34 @@ void tst_QComboBox::setModel()
     QCOMPARE(box.currentIndex(), 0);
     QVERIFY(box.model() != oldModel);
 
+    // set a new root index
+    QModelIndex rootModelIndex;
+    rootModelIndex = box.model()->index(0, 0);
+    QVERIFY(rootModelIndex.isValid());
+    box.setRootModelIndex(rootModelIndex);
+    QCOMPARE(box.rootModelIndex(), rootModelIndex);
+
+    // change the model, ensure that the root index gets reset
+    oldModel = box.model();
+    box.setModel(new QStandardItemModel(2, 1, &box));
+    QCOMPARE(box.currentIndex(), 0);
+    QVERIFY(box.model() != oldModel);
+    QVERIFY(box.rootModelIndex() != rootModelIndex);
+    QVERIFY(box.rootModelIndex() == QModelIndex());
+
     // check that setting the very same model doesn't move the current item
     box.setCurrentIndex(1);
     QCOMPARE(box.currentIndex(), 1);
     box.setModel(box.model());
     QCOMPARE(box.currentIndex(), 1);
+
+    // check that setting the very same model doesn't move the root index
+    rootModelIndex = box.model()->index(0, 0);
+    QVERIFY(rootModelIndex.isValid());
+    box.setRootModelIndex(rootModelIndex);
+    QCOMPARE(box.rootModelIndex(), rootModelIndex);
+    box.setModel(box.model());
+    QCOMPARE(box.rootModelIndex(), rootModelIndex);
 }
 
 void tst_QComboBox::setCustomModelAndView()