diff --git a/autotests/test_window_paint_data.cpp b/autotests/test_window_paint_data.cpp
index 937f136b2f..1f457d82a7 100644
--- a/autotests/test_window_paint_data.cpp
+++ b/autotests/test_window_paint_data.cpp
@@ -253,6 +253,9 @@ public:
     pid_t pid() const override {
         return 0;
     }
+    qlonglong windowId() const override {
+        return 0;
+    }
 
 private:
     qreal m_opacity = 1.0;
diff --git a/effects.cpp b/effects.cpp
index a06437ae1d..967d7170b2 100644
--- a/effects.cpp
+++ b/effects.cpp
@@ -1828,6 +1828,7 @@ TOPLEVEL_HELPER(KWaylandServer::SurfaceInterface *, surface, surface)
 TOPLEVEL_HELPER(bool, isPopupWindow, isPopupWindow)
 TOPLEVEL_HELPER(bool, isOutline, isOutline)
 TOPLEVEL_HELPER(pid_t, pid, pid)
+TOPLEVEL_HELPER(qlonglong, windowId, window)
 
 #undef TOPLEVEL_HELPER
 
diff --git a/effects.h b/effects.h
index 9b4b249d5b..dd02767bfa 100644
--- a/effects.h
+++ b/effects.h
@@ -454,6 +454,7 @@ public:
     bool isX11Client() const override;
 
     pid_t pid() const override;
+    qlonglong windowId() const override;
 
     QRect decorationInnerRect() const override;
     QByteArray readProperty(long atom, long type, int format) const override;
diff --git a/libkwineffects/kwineffects.h b/libkwineffects/kwineffects.h
index 8cecb10bd9..1c65e2846d 100644
--- a/libkwineffects/kwineffects.h
+++ b/libkwineffects/kwineffects.h
@@ -2438,6 +2438,11 @@ public:
      */
     virtual pid_t pid() const = 0;
 
+    /**
+     * @since 5.21
+     */
+    virtual qlonglong windowId() const = 0;
+
     /**
      * Can be used to by effects to store arbitrary data in the EffectWindow.
      *