diff --git a/src/events.cpp b/src/events.cpp
index c5e2b2cd08..c71ad3a950 100644
--- a/src/events.cpp
+++ b/src/events.cpp
@@ -371,7 +371,7 @@ bool X11Window::windowEvent(xcb_generic_event_t *e)
             break;
         default: {
             if (eventType == Xcb::Extensions::self()->shapeNotifyEvent()) {
-                detectShape(window());
+                detectShape();
                 Q_EMIT geometryShapeChanged(frameGeometry());
             }
             if (eventType == Xcb::Extensions::self()->damageNotifyEvent()) {
@@ -554,7 +554,7 @@ bool X11Window::windowEvent(xcb_generic_event_t *e)
     }
     default:
         if (eventType == Xcb::Extensions::self()->shapeNotifyEvent() && reinterpret_cast<xcb_shape_notify_event_t *>(e)->affected_window == window()) {
-            detectShape(window()); // workaround for #19644
+            detectShape(); // workaround for #19644
             updateShape();
         }
         if (eventType == Xcb::Extensions::self()->damageNotifyEvent() && reinterpret_cast<xcb_damage_notify_event_t *>(e)->drawable == frameId()) {
diff --git a/src/window.cpp b/src/window.cpp
index f42e2ff3cf..0732a83d6f 100644
--- a/src/window.cpp
+++ b/src/window.cpp
@@ -168,11 +168,6 @@ QDebug operator<<(QDebug debug, const Window *window)
     return debug;
 }
 
-void Window::detectShape(xcb_window_t id)
-{
-    is_shape = Xcb::Extensions::self()->hasShape(id);
-}
-
 QRectF Window::visibleGeometry() const
 {
     if (const WindowItem *item = windowItem()) {
diff --git a/src/window.h b/src/window.h
index 81d928c404..e12e01d0b6 100644
--- a/src/window.h
+++ b/src/window.h
@@ -1475,7 +1475,6 @@ Q_SIGNALS:
 
 protected:
     void setWindowHandles(xcb_window_t client);
-    void detectShape(xcb_window_t id);
     Xcb::Property fetchWmClientLeader() const;
     void readWmClientLeader(Xcb::Property &p);
     void getWmClientLeader();
@@ -1786,7 +1785,6 @@ protected:
     void cleanTabBox();
 
     QStringList m_activityList;
-    bool is_shape = false;
 
 private Q_SLOTS:
     void shadeHover();
diff --git a/src/x11window.cpp b/src/x11window.cpp
index 7040f5f288..5ca148faa7 100644
--- a/src/x11window.cpp
+++ b/src/x11window.cpp
@@ -548,7 +548,7 @@ bool X11Window::track(xcb_window_t w)
     if (Xcb::Extensions::self()->isShapeAvailable()) {
         xcb_shape_select_input(kwinApp()->x11Connection(), w, true);
     }
-    detectShape(w);
+    detectShape();
     getWmOpaqueRegion();
     getSkipCloseAnimation();
     setupCompositing();
@@ -649,7 +649,7 @@ bool X11Window::manage(xcb_window_t w, bool isMapped)
     if (Xcb::Extensions::self()->isShapeAvailable()) {
         xcb_shape_select_input(kwinApp()->x11Connection(), window(), true);
     }
-    detectShape(window());
+    detectShape();
     detectNoBorder();
     fetchIconicName();
     setClientFrameExtents(info->gtkFrameExtents());
@@ -1528,6 +1528,11 @@ void X11Window::checkNoBorder()
     setNoBorder(app_noborder);
 }
 
+void X11Window::detectShape()
+{
+    is_shape = Xcb::Extensions::self()->hasShape(window());
+}
+
 void X11Window::updateShape()
 {
     if (is_shape) {
diff --git a/src/x11window.h b/src/x11window.h
index 7f6df77e92..5797f246f6 100644
--- a/src/x11window.h
+++ b/src/x11window.h
@@ -180,6 +180,7 @@ public:
 
     void invalidateDecoration() override;
 
+    void detectShape();
     void updateShape();
 
     /// resizeWithChecks() resizes according to gravity, and checks workarea position
@@ -466,6 +467,7 @@ private:
     uint app_noborder : 1; ///< App requested no border via window type, shape extension, etc.
     uint ignore_focus_stealing : 1; ///< Don't apply focus stealing prevention to this client
     bool blocks_compositing;
+    bool is_shape = false;
 
     enum FullScreenMode {
         FullScreenNone,