diff --git a/src/widgets/widgets/qmainwindowlayout.cpp b/src/widgets/widgets/qmainwindowlayout.cpp
index 52dec2efdfb..33dda248c42 100644
--- a/src/widgets/widgets/qmainwindowlayout.cpp
+++ b/src/widgets/widgets/qmainwindowlayout.cpp
@@ -1741,6 +1741,7 @@ bool QMainWindowLayout::restoreDockWidget(QDockWidget *dockwidget)
 #if QT_CONFIG(tabbar)
 void QMainWindowLayout::tabifyDockWidget(QDockWidget *first, QDockWidget *second)
 {
+    applyRestoredState();
     addChildWidget(second);
     layoutState.dockAreaLayout.tabifyDockWidget(first, second);
     emit second->dockLocationChanged(dockWidgetArea(first));
@@ -1862,6 +1863,7 @@ void QMainWindowLayout::splitDockWidget(QDockWidget *after,
                                         QDockWidget *dockwidget,
                                         Qt::Orientation orientation)
 {
+    applyRestoredState();
     addChildWidget(dockwidget);
     layoutState.dockAreaLayout.splitDockWidget(after, dockwidget, orientation);
     emit dockwidget->dockLocationChanged(dockWidgetArea(after));
@@ -2211,6 +2213,32 @@ QLayoutItem *QMainWindowLayout::takeAt(int index)
     return nullptr;
 }
 
+
+/*!
+    \internal
+
+    restoredState stores what we earlier read from storage, but it couldn't
+    be applied as the mainwindow wasn't large enough (yet) to fit the state.
+    Usually, the restored state would be applied lazily in setGeometry below.
+    However, if the mainwindow's layout is modified (e.g. by a call to tabify or
+    splitDockWidgets), then we have to forget the restored state as it might contain
+    dangling pointers (QDockWidgetLayoutItem has a copy constructor that copies the
+    layout item pointer, and splitting or tabify might have to delete some of those
+    layout structures).
+
+    Functions that might result in the QMainWindowLayoutState storing dangling pointers
+    have to call this function first, so that the restoredState becomes the actual state
+    first, and is forgotten afterwards.
+*/
+void QMainWindowLayout::applyRestoredState()
+{
+    if (restoredState) {
+        layoutState = *restoredState;
+        restoredState.reset();
+        discardRestoredStateTimer.stop();
+    }
+}
+
 void QMainWindowLayout::setGeometry(const QRect &_r)
 {
     if (savedState.isValid())
diff --git a/src/widgets/widgets/qmainwindowlayout_p.h b/src/widgets/widgets/qmainwindowlayout_p.h
index 72bb9f23846..83d41fa5814 100644
--- a/src/widgets/widgets/qmainwindowlayout_p.h
+++ b/src/widgets/widgets/qmainwindowlayout_p.h
@@ -587,6 +587,7 @@ public:
     QLayoutItem *unplug(QWidget *widget, QDockWidgetPrivate::DragScope scope);
     void revert(QLayoutItem *widgetItem);
     void applyState(QMainWindowLayoutState &newState, bool animate = true);
+    void applyRestoredState();
     void restore(bool keepSavedState = false);
     void animationFinished(QWidget *widget);
 
diff --git a/tests/auto/widgets/widgets/qmainwindow/tst_qmainwindow.cpp b/tests/auto/widgets/widgets/qmainwindow/tst_qmainwindow.cpp
index d2e5e86dea2..b5457e5e722 100644
--- a/tests/auto/widgets/widgets/qmainwindow/tst_qmainwindow.cpp
+++ b/tests/auto/widgets/widgets/qmainwindow/tst_qmainwindow.cpp
@@ -104,6 +104,7 @@ private slots:
     void restoreStateFromPreviousVersion();
     void restoreStateSizeChanged_data();
     void restoreStateSizeChanged();
+    void restoreAndModify();
     void createPopupMenu();
     void hideBeforeLayout();
 #ifdef QT_BUILD_INTERNAL
@@ -1476,6 +1477,70 @@ void tst_QMainWindow::restoreStateSizeChanged()
     }
 }
 
+/*!
+    If a main window's state is restored but also modified, then we
+    might have to forget the restored state to avoid dangling pointers.
+    See comment in QMainWindowLayout::applyRestoredState() and QTBUG-120025.
+*/
+void tst_QMainWindow::restoreAndModify()
+{
+    class MainWindow : public QMainWindow
+    {
+    public:
+        MainWindow()
+        {
+            setCentralWidget(new QTextEdit);
+
+            customers = new QDockWidget(tr("Customers"), this);
+            customers->setObjectName("Customers");
+            customers->setAllowedAreas(Qt::LeftDockWidgetArea |
+                                                  Qt::RightDockWidgetArea);
+            customers->setWidget(new QTextEdit);
+            addDockWidget(Qt::RightDockWidgetArea, customers);
+
+            paragraphs = new QDockWidget(tr("Paragraphs"), this);
+            paragraphs->setObjectName("Paragraphs");
+            paragraphs->setWidget(new QTextEdit);
+            addDockWidget(Qt::RightDockWidgetArea, paragraphs);
+        }
+
+        void restore()
+        {
+            if (!savedGeometry.isEmpty())
+                restoreGeometry(savedGeometry);
+            setWindowState(Qt::WindowMaximized);
+            if (!savedState.isEmpty())
+                restoreState(savedState);
+
+            tabifyDockWidget(customers, paragraphs);
+        }
+    protected:
+        void closeEvent(QCloseEvent *event) override
+        {
+            savedGeometry = saveGeometry();
+            savedState = saveState();
+
+            return QMainWindow::closeEvent(event);
+        }
+    private:
+        QByteArray savedGeometry;
+        QByteArray savedState;
+
+        QDockWidget *customers;
+        QDockWidget *paragraphs;
+
+    } mainWindow;
+
+    mainWindow.restore();
+    mainWindow.show();
+    QVERIFY(QTest::qWaitForWindowExposed(&mainWindow));
+    mainWindow.close();
+
+    mainWindow.restore();
+    mainWindow.show();
+    QVERIFY(QTest::qWaitForWindowExposed(&mainWindow));
+}
+
 void tst_QMainWindow::createPopupMenu()
 {
     {