diff --git a/GeoModelCore/GeoModelKernel/GeoModelKernel/GeoLogVol.h b/GeoModelCore/GeoModelKernel/GeoModelKernel/GeoLogVol.h
index eddc8f399cf241e0d10e237819942397d8f55074..a590f630c2289b1d1d7be9fac6415de9b9fad5d4 100644
--- a/GeoModelCore/GeoModelKernel/GeoModelKernel/GeoLogVol.h
+++ b/GeoModelCore/GeoModelKernel/GeoModelKernel/GeoLogVol.h
@@ -55,6 +55,7 @@ class GeoLogVol : public RCBase
 
   //	Material composition of this volume.
   mutable GeoIntrusivePtr<const GeoMaterial> m_material{};
+  std::shared_mutex m_mutex{};
 
   //	Shape of this volume.
   GeoIntrusivePtr<const GeoShape> m_shape{};