diff --git a/composite.cpp b/composite.cpp
index c36d83164a..4c848f04d5 100644
--- a/composite.cpp
+++ b/composite.cpp
@@ -296,6 +296,7 @@ void Compositor::startupWithWorkspace()
     if (!m_starting) {
         return;
     }
+    Workspace::self()->markXStackingOrderAsDirty();
     Q_ASSERT(m_scene);
     connect(workspace(), &Workspace::destroyed, this, [this] { compositeTimer.stop(); });
     claimCompositorSelection();
diff --git a/layers.cpp b/layers.cpp
index 8290bf3730..1734d0cb6c 100644
--- a/layers.cpp
+++ b/layers.cpp
@@ -687,18 +687,23 @@ bool Workspace::keepTransientAbove(const AbstractClient* mainwindow, const Abstr
 // Returns all windows in their stacking order on the root window.
 ToplevelList Workspace::xStackingOrder() const
 {
-    if (!x_stacking_dirty)
-        return x_stacking;
-    x_stacking_dirty = false;
+    if (m_xStackingQueryTree) {
+        const_cast<Workspace*>(this)->updateXStackingOrder();
+    }
+    return x_stacking;
+}
+
+void Workspace::updateXStackingOrder()
+{
     x_stacking.clear();
-    Xcb::Tree tree(rootWindow());
+    std::unique_ptr<Xcb::Tree> tree{std::move(m_xStackingQueryTree)};
     // use our own stacking order, not the X one, as they may differ
     foreach (Toplevel * c, stacking_order)
     x_stacking.append(c);
 
-    if (!tree.isNull()) {
-        xcb_window_t *windows = tree.children();
-        const auto count = tree->children_len;
+    if (!tree->isNull()) {
+        xcb_window_t *windows = tree->children();
+        const auto count = tree->data()->children_len;
         int foundUnmanagedCount = unmanaged.count();
         for (unsigned int i = 0;
                 i < count;
@@ -724,7 +729,6 @@ ToplevelList Workspace::xStackingOrder() const
             }
         }
     }
-    return x_stacking;
 }
 
 //*******************************
diff --git a/workspace.cpp b/workspace.cpp
index c7c9d1dff7..5f60a6af9e 100644
--- a/workspace.cpp
+++ b/workspace.cpp
@@ -112,7 +112,6 @@ Workspace::Workspace(const QString &sessionKey)
     , movingClient(0)
     , delayfocus_client(0)
     , force_restacking(false)
-    , x_stacking_dirty(true)
     , showing_desktop(false)
     , was_user_interaction(false)
     , session_saving(false)
@@ -1768,7 +1767,7 @@ Toplevel *Workspace::findInternal(QWindow *w) const
 
 void Workspace::markXStackingOrderAsDirty()
 {
-    x_stacking_dirty = true;
+    m_xStackingQueryTree.reset(new Xcb::Tree(rootWindow()));
 }
 
 } // namespace
diff --git a/workspace.h b/workspace.h
index b4487dc51e..e6a983496d 100644
--- a/workspace.h
+++ b/workspace.h
@@ -32,6 +32,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include <QVector>
 // std
 #include <functional>
+#include <memory>
 
 // TODO: Cleanup the order of things in this .h file
 
@@ -47,6 +48,7 @@ namespace KWin
 
 namespace Xcb
 {
+class Tree;
 class Window;
 }
 
@@ -365,6 +367,8 @@ public:
     void registerEventFilter(X11EventFilter *filter);
     void unregisterEventFilter(X11EventFilter *filter);
 
+    void markXStackingOrderAsDirty();
+
 public Q_SLOTS:
     void performWindowOperation(KWin::AbstractClient* c, Options::WindowOperation op);
     // Keybindings
@@ -546,7 +550,7 @@ private:
     static NET::WindowType txtToWindowType(const char* txt);
     static bool sessionInfoWindowTypeMatch(Client* c, SessionInfo* info);
 
-    void markXStackingOrderAsDirty();
+    void updateXStackingOrder();
 
     AbstractClient* active_client;
     AbstractClient* last_active_client;
@@ -567,8 +571,8 @@ private:
     ToplevelList unconstrained_stacking_order; // Topmost last
     ToplevelList stacking_order; // Topmost last
     bool force_restacking;
-    mutable ToplevelList x_stacking; // From XQueryTree()
-    mutable bool x_stacking_dirty;
+    ToplevelList x_stacking; // From XQueryTree()
+    std::unique_ptr<Xcb::Tree> m_xStackingQueryTree;
     QList<AbstractClient*> should_get_focus; // Last is most recent
     QList<AbstractClient*> attention_chain;