diff --git a/src/common/QskScaleEngine.h b/src/common/QskScaleEngine.h
index 5d2b6345..334ba809 100644
--- a/src/common/QskScaleEngine.h
+++ b/src/common/QskScaleEngine.h
@@ -59,4 +59,6 @@ class QSK_EXPORT QskScaleEngine
     Attributes m_attributes;
 };
 
+Q_DECLARE_OPERATORS_FOR_FLAGS( QskScaleEngine::Attributes )
+
 #endif