diff --git a/src/common/QskAspect.h b/src/common/QskAspect.h
index 61dcb3d7..f98569eb 100644
--- a/src/common/QskAspect.h
+++ b/src/common/QskAspect.h
@@ -588,6 +588,11 @@ QSK_EXPORT void qskDebugAspect( QDebug, const QMetaObject*, QskAspect );
         QskAspect::registerState( &type::staticMetaObject, value, #type "::" #name );
 
 #define QSK_SYSTEM_STATE( type, name, value ) \
+    static_assert( \
+        ( value >= QskAspect::FirstSystemState && value < QskAspect::FirstUserState ) || \
+        ( value > QskAspect::LastUserState && value <= QskAspect::LastSystemState ), \
+        "Invalid system state" \
+    ); \
     const QskAspect::State type::name = \
         QskAspect::registerState( &type::staticMetaObject, value, #type "::" #name );
 
diff --git a/src/controls/QskAbstractButton.cpp b/src/controls/QskAbstractButton.cpp
index abda742e..70b8062c 100644
--- a/src/controls/QskAbstractButton.cpp
+++ b/src/controls/QskAbstractButton.cpp
@@ -10,24 +10,25 @@
 
 #include <qbasictimer.h>
 
+// Flat/Checkable are no states - we need to get rid of them. TODO ...
 QSK_SYSTEM_STATE( QskAbstractButton, Flat, QskAspect::FirstSystemState << 1 )
 #if 1
 // Wrong: we are overlapping with the user states, TODO ...
-QSK_SYSTEM_STATE( QskAbstractButton, Checked, QskAspect::LastSystemState >> 4 )
+QSK_STATE( QskAbstractButton, Checked, QskAspect::LastUserState )
 #endif
 QSK_SYSTEM_STATE( QskAbstractButton, Pressed, QskAspect::LastSystemState >> 3 )
 QSK_SYSTEM_STATE( QskAbstractButton, Checkable, QskAspect::LastSystemState >> 2 )
 
 static QskAbstractButton* qskCheckedSibling( const QskAbstractButton* button )
 {
-    QQuickItem* parentItem = button->parentItem();
+    const auto parentItem = button->parentItem();
     if ( parentItem == nullptr )
         return nullptr;
 
     const auto siblings = parentItem->childItems();
-    for ( QQuickItem* sibling : siblings )
+    for ( auto sibling : siblings )
     {
-        if ( QskAbstractButton* btn = qobject_cast< QskAbstractButton* >( sibling ) )
+        if ( auto btn = qobject_cast< QskAbstractButton* >( sibling ) )
         {
             if ( btn != button && btn->exclusive() && btn->isChecked() )
                 return btn;
diff --git a/src/controls/QskSlider.cpp b/src/controls/QskSlider.cpp
index b23c5217..c5085448 100644
--- a/src/controls/QskSlider.cpp
+++ b/src/controls/QskSlider.cpp
@@ -16,8 +16,8 @@ QSK_SUBCONTROL( QskSlider, Scale )
 QSK_SUBCONTROL( QskSlider, Handle )
 
 QSK_SYSTEM_STATE( QskSlider, Pressed, QskAspect::FirstSystemState << 2 )
-QSK_SYSTEM_STATE( QskSlider, Minimum, QskAspect::FirstSystemState << 3 )
-QSK_SYSTEM_STATE( QskSlider, Maximum, QskAspect::FirstSystemState << 4 )
+QSK_SYSTEM_STATE( QskSlider, Minimum, QskAspect::LastUserState << 1 )
+QSK_SYSTEM_STATE( QskSlider, Maximum, QskAspect::LastUserState << 2 )
 
 class QskSlider::PrivateData
 {