diff --git a/src/controllers/FloatingWindow.cpp b/src/controllers/FloatingWindow.cpp
index 5a11a925..708fcc4b 100644
--- a/src/controllers/FloatingWindow.cpp
+++ b/src/controllers/FloatingWindow.cpp
@@ -525,9 +525,10 @@ LayoutSaver::FloatingWindow FloatingWindow::serialize() const
     fw.affinities = affinities();
     fw.windowState = windowStateOverride();
 
-    auto parentView = view()->parentView();
-    auto mainWindow = parentView ? parentView->asMainWindowController() : nullptr;
-    fw.parentIndex = mainWindow ? DockRegistry::self()->mainwindows().indexOf(mainWindow) : -1;
+    Window::Ptr window = view()->window();
+    Window::Ptr transientParentWindow = window ? window->transientParent() : nullptr;
+    auto transientMainWindow = transientParentWindow ? DockRegistry::self()->mainWindowForHandle(transientParentWindow) : nullptr;
+    fw.parentIndex = transientMainWindow ? DockRegistry::self()->mainwindows().indexOf(transientMainWindow) : -1;
 
     return fw;
 }
diff --git a/tests/tst_docks.cpp b/tests/tst_docks.cpp
index 9a1d5b98..c0074494 100644
--- a/tests/tst_docks.cpp
+++ b/tests/tst_docks.cpp
@@ -182,6 +182,8 @@ void TestDocks::tst_restoreSimple()
     QVERIFY(fw2->isVisible());
     QVERIFY(fw2->view()->isRootView());
     QCOMPARE(fw2->pos(), dock2FloatingPoint);
+
+    QVERIFY(fw2->view()->window()->transientParent());
     QVERIFY(m->view()->window()->equals(fw2->view()->window()->transientParent()));
     QVERIFY(dock2->isFloating());
     QVERIFY(dock2->isVisible());