diff --git a/src/dbus/qdbusargument.h b/src/dbus/qdbusargument.h
index ac650d5f62..94a89a4e08 100644
--- a/src/dbus/qdbusargument.h
+++ b/src/dbus/qdbusargument.h
@@ -158,6 +158,7 @@ QT_END_NAMESPACE
 Q_DECLARE_METATYPE(QDBusArgument)
 QT_BEGIN_NAMESPACE
 
+// ### Qt6: remove the defaulted T * = nullptr from these two (MSVC6 work-around):
 template<typename T> inline T qdbus_cast(const QDBusArgument &arg, T * = nullptr)
 {
     T item;