diff --git a/src/widgets/widgets/qdockarealayout.cpp b/src/widgets/widgets/qdockarealayout.cpp
index da0e9871715..32d0f9b345a 100644
--- a/src/widgets/widgets/qdockarealayout.cpp
+++ b/src/widgets/widgets/qdockarealayout.cpp
@@ -19,6 +19,11 @@
 #include "qdockwidget_p.h"
 #include <private/qlayoutengine_p.h>
 
+#if QT_CONFIG(toolbar)
+#include "qtoolbar.h"
+#include "qtoolbarlayout_p.h"
+#endif
+
 #include <qpainter.h>
 #include <qstyleoption.h>
 
@@ -2036,6 +2041,30 @@ bool QDockAreaLayoutInfo::restoreState(QDataStream &stream, QList<QDockWidget*>
 }
 
 #if QT_CONFIG(tabbar)
+
+static void raiseSeparatorWidget(QWidget *separatorWidget)
+{
+    Q_ASSERT(separatorWidget);
+
+#if QT_CONFIG(toolbar)
+    // Raise the separator widget, but make sure it doesn't go above
+    // an expanded toolbar, as that would break mouse event hit testing.
+    Q_ASSERT(separatorWidget->parent());
+    const auto toolBars = separatorWidget->parent()->findChildren<QToolBar*>(Qt::FindDirectChildrenOnly);
+    for (auto *toolBar : toolBars) {
+        if (auto *toolBarLayout = qobject_cast<QToolBarLayout*>(toolBar->layout())) {
+            if (toolBarLayout->expanded) {
+                separatorWidget->stackUnder(toolBar);
+                return;
+            }
+        }
+    }
+#endif
+
+    separatorWidget->raise();
+}
+
+
 void QDockAreaLayoutInfo::updateSeparatorWidgets() const
 {
     if (tabbed) {
@@ -2077,7 +2106,7 @@ void QDockAreaLayoutInfo::updateSeparatorWidgets() const
         j++;
 
         Q_ASSERT(sepWidget);
-        sepWidget->raise();
+        raiseSeparatorWidget(sepWidget);
 
         QRect sepRect = separatorRect(i).adjusted(-2, -2, 2, 2);
         sepWidget->setGeometry(sepRect);
@@ -3362,7 +3391,7 @@ void QDockAreaLayout::updateSeparatorWidgets() const
         j++;
 
         Q_ASSERT(sepWidget);
-        sepWidget->raise();
+        raiseSeparatorWidget(sepWidget);
 
         QRect sepRect = separatorRect(i).adjusted(-2, -2, 2, 2);
         sepWidget->setGeometry(sepRect);
diff --git a/src/widgets/widgets/qmainwindowlayout.cpp b/src/widgets/widgets/qmainwindowlayout.cpp
index 34c18c8f886..ee854615e90 100644
--- a/src/widgets/widgets/qmainwindowlayout.cpp
+++ b/src/widgets/widgets/qmainwindowlayout.cpp
@@ -274,6 +274,14 @@ public:
 
     QDockAreaLayoutInfo *dockAreaLayoutInfo() { return &layoutState; }
 
+#if QT_CONFIG(toolbar)
+    QToolBarAreaLayout *toolBarAreaLayout()
+    {
+        auto *mainWindow = static_cast<QMainWindow*>(parentWidget());
+        return qt_mainwindow_layout(mainWindow)->toolBarAreaLayout();
+    }
+#endif
+
     bool nativeWindowDeco() const
     {
         return groupWindow()->hasNativeDecos();
diff --git a/src/widgets/widgets/qmainwindowlayout_p.h b/src/widgets/widgets/qmainwindowlayout_p.h
index 55a27e4849d..f4211046e1c 100644
--- a/src/widgets/widgets/qmainwindowlayout_p.h
+++ b/src/widgets/widgets/qmainwindowlayout_p.h
@@ -43,6 +43,7 @@ struct QDockWidgetPrivate {
 #endif
 #if QT_CONFIG(toolbar)
 #include "qtoolbararealayout_p.h"
+#include "qtoolbar.h"
 #endif
 
 #include <QtCore/qloggingcategory.h>
@@ -92,6 +93,9 @@ public:
     bool endSeparatorMove(const QPoint &pos);
     bool windowEvent(QEvent *e);
 
+private:
+    QList<int> findSeparator(const QPoint &pos) const;
+
 #endif // QT_CONFIG(dockwidget)
 
 };
@@ -142,7 +146,7 @@ void QMainWindowLayoutSeparatorHelper<Layout>::adjustCursor(const QPoint &pos)
                 w->unsetCursor();
         }
     } else if (movingSeparator.isEmpty()) { // Don't change cursor when moving separator
-        QList<int> pathToSeparator = layout()->dockAreaLayoutInfo()->findSeparator(pos);
+        QList<int> pathToSeparator = findSeparator(pos);
 
         if (pathToSeparator != hoverSeparator) {
             if (!hoverSeparator.isEmpty())
@@ -279,10 +283,35 @@ bool QMainWindowLayoutSeparatorHelper<Layout>::windowEvent(QEvent *event)
     return false;
 }
 
+template <typename Layout>
+QList<int> QMainWindowLayoutSeparatorHelper<Layout>::findSeparator(const QPoint &pos) const
+{
+    Layout *layout = const_cast<Layout*>(this->layout());
+#if QT_CONFIG(toolbar)
+    QToolBarAreaLayout *toolBarAreaLayout = layout->toolBarAreaLayout();
+    if (!toolBarAreaLayout->isEmpty()) {
+        // We might have a toolbar that is currently expanded, covering
+        // parts of the dock area, in which case we don't want the dock
+        // area layout to treat mouse events for the expanded toolbar as
+        // hitting a separator.
+        const QWidget *widget = layout->window();
+        QWidget *childWidget = widget->childAt(pos);
+        while (childWidget && childWidget != widget) {
+            if (auto *toolBar = qobject_cast<QToolBar*>(childWidget)) {
+                if (!toolBarAreaLayout->indexOf(toolBar).isEmpty())
+                    return {};
+            }
+            childWidget = childWidget->parentWidget();
+        }
+    }
+#endif
+    return layout->dockAreaLayoutInfo()->findSeparator(pos);
+}
+
 template <typename Layout>
 bool QMainWindowLayoutSeparatorHelper<Layout>::startSeparatorMove(const QPoint &pos)
 {
-    movingSeparator = layout()->dockAreaLayoutInfo()->findSeparator(pos);
+    movingSeparator = findSeparator(pos);
 
     if (movingSeparator.isEmpty())
         return false;
@@ -493,6 +522,7 @@ public:
     void removeToolBar(QToolBar *toolbar);
     void toggleToolBarsVisible();
     void moveToolBar(QToolBar *toolbar, int pos);
+    QToolBarAreaLayout *toolBarAreaLayout() { return &layoutState.toolBarAreaLayout; }
 #endif
 
     // dock widgets
diff --git a/src/widgets/widgets/qtoolbarlayout_p.h b/src/widgets/widgets/qtoolbarlayout_p.h
index a7d3810d619..7915af1e44b 100644
--- a/src/widgets/widgets/qtoolbarlayout_p.h
+++ b/src/widgets/widgets/qtoolbarlayout_p.h
@@ -38,7 +38,7 @@ public:
     bool customWidget;
 };
 
-class QToolBarLayout : public QLayout
+class Q_AUTOTEST_EXPORT QToolBarLayout : public QLayout
 {
     Q_OBJECT
 
diff --git a/tests/auto/widgets/widgets/qmainwindow/tst_qmainwindow.cpp b/tests/auto/widgets/widgets/qmainwindow/tst_qmainwindow.cpp
index 093af90d1cb..bf0f58587a4 100644
--- a/tests/auto/widgets/widgets/qmainwindow/tst_qmainwindow.cpp
+++ b/tests/auto/widgets/widgets/qmainwindow/tst_qmainwindow.cpp
@@ -22,6 +22,8 @@
 #include <qscreen.h>
 #include <private/qmainwindowlayout_p.h>
 #include <private/qdockarealayout_p.h>
+#include <private/qtoolbarlayout_p.h>
+#include <private/qtoolbarextension_p.h>
 
 #if QT_CONFIG(tabbar)
 #include <qtabbar.h>
@@ -133,6 +135,9 @@ private slots:
 #if QT_CONFIG(dockwidget) && QT_CONFIG(tabbar)
     void QTBUG52175_tabifiedDockWidgetActivated();
 #endif
+#ifdef QT_BUILD_INTERNAL
+    void expandedToolBarHitTesting();
+#endif
 };
 
 
@@ -2255,5 +2260,58 @@ void tst_QMainWindow::QTBUG52175_tabifiedDockWidgetActivated()
 }
 #endif
 
+#ifdef QT_BUILD_INTERNAL
+void tst_QMainWindow::expandedToolBarHitTesting()
+{
+    QMainWindow mainWindow;
+    if (mainWindow.style()->pixelMetric(
+        QStyle::PM_DockWidgetSeparatorExtent, nullptr, &mainWindow) != 1) {
+        QSKIP("Style does not trigger the use of qt_qmainwindow_extended_splitter");
+    }
+
+    mainWindow.setAnimated(false);
+
+    auto *dockWidget = new QDockWidget(&mainWindow);
+    dockWidget->setWidget(new QWidget(dockWidget));
+    mainWindow.addDockWidget(Qt::RightDockWidgetArea, dockWidget);
+
+    auto *toolBar = new QToolBar(&mainWindow);
+    for (int i = 0; i < 10; ++i)
+        toolBar->addWidget(new QLabel(QString("Label %1").arg(i)));
+    mainWindow.addToolBar(toolBar);
+
+    auto *centralWidget = new QWidget(&mainWindow);
+    centralWidget->setMinimumSize(QSize(100, 100));
+    mainWindow.setCentralWidget(centralWidget);
+
+    mainWindow.resize(centralWidget->minimumSize());
+    mainWindow.show();
+    QVERIFY(QTest::qWaitForWindowActive(&mainWindow));
+
+    auto *toolBarExtension = toolBar->findChild<QToolBarExtension*>();
+    QVERIFY(toolBarExtension);
+    QPoint buttonCenter = toolBarExtension->parentWidget()->mapTo(&mainWindow, toolBarExtension->geometry().center());
+    QTest::mouseMove(mainWindow.windowHandle(), buttonCenter);
+    QTest::mouseClick(mainWindow.windowHandle(), Qt::LeftButton, Qt::NoModifier, buttonCenter);
+
+    auto *toolBarLayout = static_cast<QToolBarLayout*>(toolBar->layout());
+    QVERIFY(toolBarLayout);
+    QTRY_COMPARE(toolBarLayout->expanded, true);
+
+    auto *splitter = mainWindow.findChild<QWidget*>("qt_qmainwindow_extended_splitter");
+    QVERIFY(splitter);
+    QCOMPARE(splitter->parentWidget(), &mainWindow);
+
+    // Moving the mouse over the splitter when it's covered by the toolbar
+    // extension area should not trigger a closing of the extension area.
+    QTest::mouseMove(mainWindow.windowHandle(), splitter->geometry().center());
+    QCOMPARE(toolBarLayout->expanded, true);
+
+    // Nor should it result in a split cursor shape, indicating we can move
+    // the splitter.
+    QCOMPARE(mainWindow.cursor().shape(), Qt::ArrowCursor);
+}
+#endif // QT_BUILD_INTERNAL
+
 QTEST_MAIN(tst_QMainWindow)
 #include "tst_qmainwindow.moc"