diff --git a/src/widgets/widgets/qmdiarea.cpp b/src/widgets/widgets/qmdiarea.cpp
index 2978893205..79b83453ac 100644
--- a/src/widgets/widgets/qmdiarea.cpp
+++ b/src/widgets/widgets/qmdiarea.cpp
@@ -2376,6 +2376,11 @@ void QMdiArea::showEvent(QShowEvent *showEvent)
         for (QMdiSubWindow *window : copy) {
             if (!window)
                 continue;
+            if (d->viewMode == TabbedView && window->d_func()->isActive && !d->active) {
+                d->showActiveWindowMaximized = true;
+                d->emitWindowActivated(window); // Also maximizes the window
+                continue;
+            }
             if (!window->testAttribute(Qt::WA_Resized)) {
                 QSize newSize(window->sizeHint().boundedTo(viewport()->size()));
                 window->resize(newSize.expandedTo(qSmartMinSize(window)));
diff --git a/src/widgets/widgets/qmdisubwindow.h b/src/widgets/widgets/qmdisubwindow.h
index a34c0249ec..4227f02dac 100644
--- a/src/widgets/widgets/qmdisubwindow.h
+++ b/src/widgets/widgets/qmdisubwindow.h
@@ -101,6 +101,7 @@ private:
     Q_PRIVATE_SLOT(d_func(), void _q_enterInteractiveMode())
     Q_PRIVATE_SLOT(d_func(), void _q_processFocusChanged(QWidget *, QWidget *))
     friend class QMdiAreaPrivate;
+    friend class QMdiArea;
 #if QT_CONFIG(tabbar)
     friend class QMdiAreaTabBar;
 #endif
diff --git a/tests/auto/widgets/widgets/qmdiarea/tst_qmdiarea.cpp b/tests/auto/widgets/widgets/qmdiarea/tst_qmdiarea.cpp
index 1aa99f27cf..af604372ea 100644
--- a/tests/auto/widgets/widgets/qmdiarea/tst_qmdiarea.cpp
+++ b/tests/auto/widgets/widgets/qmdiarea/tst_qmdiarea.cpp
@@ -260,6 +260,7 @@ private slots:
     void task_236750();
     void qtbug92240_title_data();
     void qtbug92240_title();
+    void tabbedview_singleSubWindow();
     void tabbedview_activefirst();
     void tabbedview_activesecond();
     void tabbedview_activethird();
@@ -2728,6 +2729,21 @@ void tst_QMdiArea::qtbug92240_title()
     QTRY_COMPARE(w.windowTitle(), QLatin1String("QTBUG-92240 - [2]"));
 }
 
+void tst_QMdiArea::tabbedview_singleSubWindow()
+{
+    // With only one sub-window, setViewMode() before addSubWindow(); and addSubWindow()
+    // before show(), ensure the sub-window is properly activated.
+    QMdiArea mdiArea;
+    mdiArea.setViewMode(QMdiArea::TabbedView);
+    auto *w = new QWidget(&mdiArea);
+    mdiArea.addSubWindow(w);
+    mdiArea.show();
+    QVERIFY(QTest::qWaitForWindowExposed(&mdiArea));
+    auto *sub = mdiArea.subWindowList().at(0);
+    QCOMPARE(mdiArea.activeSubWindow(), sub);
+    QVERIFY(sub->isMaximized());
+}
+
 static void setupMdiAreaWithTabbedView(QMdiArea &mdiArea)
 {
     mdiArea.setViewMode(QMdiArea::TabbedView);