diff --git a/scene.h b/scene.h
--- a/scene.h
+++ b/scene.h
@@ -336,6 +336,7 @@
     Shadow* shadow();
     void referencePreviousPixmap();
     void unreferencePreviousPixmap();
+    void invalidateQuadsCache();
 protected:
     WindowQuadList makeQuads(WindowQuadType type, const QRegion& reg, const QPoint &textureOffset = QPoint(0, 0), qreal textureScale = 1.0) const;
     WindowQuadList makeDecorationQuads(const QRect *rects, const QRegion &region, qreal textureScale = 1.0) const;
diff --git a/scene.cpp b/scene.cpp
--- a/scene.cpp
+++ b/scene.cpp
@@ -405,6 +405,11 @@
     c->effectWindow()->setSceneWindow(w);
     c->getShadow();
     w->updateShadow(c->shadow());
+    connect(c, &Toplevel::shadowChanged, this,
+        [w] {
+            w->invalidateQuadsCache();
+        }
+    );
 }
 
 void Scene::windowClosed(Toplevel *c, Deleted *deleted)
@@ -732,7 +737,7 @@
     // it is created on-demand and cached, simply
     // reset the flag
     shape_valid = false;
-    cached_quad_list.reset();
+    invalidateQuadsCache();
 }
 
 // Find out the shape of the window using the XShape extension
@@ -936,6 +941,11 @@
     return list;
 }
 
+void Scene::Window::invalidateQuadsCache()
+{
+    cached_quad_list.reset();
+}
+
 WindowQuadList Scene::Window::makeQuads(WindowQuadType type, const QRegion& reg, const QPoint &textureOffset, qreal scale) const
 {
     WindowQuadList ret;
diff --git a/shadow.cpp b/shadow.cpp
--- a/shadow.cpp
+++ b/shadow.cpp
@@ -65,9 +65,7 @@
     }
     if (toplevel->effectWindow() && toplevel->effectWindow()->sceneWindow()) {
         toplevel->effectWindow()->sceneWindow()->updateShadow(shadow);
-    }
-    if (toplevel->effectWindow()) {
-        toplevel->effectWindow()->buildQuads(true);
+        emit toplevel->shadowChanged();
     }
     return shadow;
 }
@@ -333,52 +331,52 @@
 
 bool Shadow::updateShadow()
 {
-    auto clear = [this]() {
-        if (m_topLevel && m_topLevel->effectWindow() && m_topLevel->effectWindow()->sceneWindow() &&
-                                            m_topLevel->effectWindow()->sceneWindow()->shadow()) {
+    auto clear = [this] {
+        if (m_topLevel && m_topLevel->shadow()) {
             auto w = m_topLevel->effectWindow();
             // this also deletes the shadow
             w->sceneWindow()->updateShadow(nullptr);
-            w->buildQuads(true);
+            emit m_topLevel->shadowChanged();
         }
     };
+
+    if (!m_topLevel) {
+        return false;
+    }
+
     if (m_decorationShadow) {
         if (AbstractClient *c = qobject_cast<AbstractClient*>(m_topLevel)) {
             if (c->decoration()) {
                 if (init(c->decoration())) {
-                    if (m_topLevel && m_topLevel->effectWindow())
-                        m_topLevel->effectWindow()->buildQuads(true);
+                    emit m_topLevel->shadowChanged();
                     return true;
                 }
             }
         }
         clear();
         return false;
     }
+
     if (waylandServer()) {
         if (m_topLevel && m_topLevel->surface()) {
             if (const auto &s = m_topLevel->surface()->shadow()) {
                 if (init(s)) {
-                    if (m_topLevel->effectWindow()) {
-                        m_topLevel->effectWindow()->buildQuads(true);
-                    }
+                    emit m_topLevel->shadowChanged();
                     return true;
                 }
             }
         }
     }
-    if (!m_topLevel) {
-        clear();
-        return false;
-    }
+
     auto data = Shadow::readX11ShadowProperty(m_topLevel->window());
     if (data.isEmpty()) {
         clear();
         return false;
     }
+
     init(data);
-    if (m_topLevel && m_topLevel->effectWindow())
-        m_topLevel->effectWindow()->buildQuads(true);
+    emit m_topLevel->shadowChanged();
+
     return true;
 }
 
diff --git a/toplevel.h b/toplevel.h
--- a/toplevel.h
+++ b/toplevel.h
@@ -518,6 +518,12 @@
      */
     void screenScaleChanged();
 
+    /**
+     * Emitted whenever the client's shadow changes.
+     * @since 5.15
+     **/
+    void shadowChanged();
+
 protected Q_SLOTS:
     /**
      * Checks whether the screen number for this Toplevel changed and updates if needed.