diff --git a/src/kmainwindow.h b/src/kmainwindow.h
--- a/src/kmainwindow.h
+++ b/src/kmainwindow.h
@@ -47,7 +47,7 @@
     inline const classname ## Private *k_func() const { return reinterpret_cast<classname ## Private *>(k_ptr); } \
     friend class classname ## Private;
 
-// This is mostly from KDE3. TODO KDE5: remove the constructor parameter.
+// TODO KF6: remove
 #define KDE_DEFAULT_WINDOWFLAGS 0
 
 /**
@@ -151,7 +151,7 @@
      * for the composer windows "composer#".
      *
      */
-    explicit KMainWindow(QWidget *parent = nullptr, Qt::WindowFlags f = KDE_DEFAULT_WINDOWFLAGS);
+    explicit KMainWindow(QWidget *parent = nullptr, Qt::WindowFlags f = Qt::WindowFlags());
 
     /**
      * \brief Destructor.
diff --git a/src/kxmlguiwindow.h b/src/kxmlguiwindow.h
--- a/src/kxmlguiwindow.h
+++ b/src/kxmlguiwindow.h
@@ -40,6 +40,7 @@
 class KToolBar;
 class KXmlGuiWindowPrivate;
 
+// TODO KF6: remove
 #define KDE_DEFAULT_WINDOWFLAGS 0
 
 /**
@@ -103,7 +104,7 @@
      * for the composer windows "composer#".
      *
      */
-    explicit KXmlGuiWindow(QWidget *parent = nullptr, Qt::WindowFlags f = KDE_DEFAULT_WINDOWFLAGS);
+    explicit KXmlGuiWindow(QWidget *parent = nullptr, Qt::WindowFlags f = Qt::WindowFlags());
 
     /**
      * \brief Destructor.