diff --git a/libkwineffects/kwineffects.h b/libkwineffects/kwineffects.h
index 2b83bbd451..ec74651a45 100644
--- a/libkwineffects/kwineffects.h
+++ b/libkwineffects/kwineffects.h
@@ -1722,6 +1722,7 @@ private:
 class KWIN_EXPORT WindowQuad
 {
 public:
+    explicit WindowQuad();
     explicit WindowQuad(WindowQuadType type, int id = -1);
     WindowQuad makeSubQuad(double x1, double y1, double x2, double y2) const;
     WindowVertex& operator[](int index);
@@ -1748,7 +1749,7 @@ private:
 };
 
 class KWIN_EXPORT WindowQuadList
-    : public QList< WindowQuad >
+    : public QVector<WindowQuad>
 {
 public:
     WindowQuadList splitAtX(double x) const;
@@ -2642,6 +2643,13 @@ void WindowVertex::setY(double y)
  WindowQuad
 ***************************************************************/
 
+inline
+WindowQuad::WindowQuad()
+    : quadType(WindowQuadError)
+    , quadID(-1)
+{
+}
+
 inline
 WindowQuad::WindowQuad(WindowQuadType t, int id)
     : quadType(t)