diff --git a/DDCore/src/Volumes.cpp b/DDCore/src/Volumes.cpp
index 8d61a0462632788daf9114dafd148f758bc68bce..96f789940b9027535d67ade03f8f90937174a2ad 100644
--- a/DDCore/src/Volumes.cpp
+++ b/DDCore/src/Volumes.cpp
@@ -31,7 +31,9 @@
 using namespace std;
 using namespace DD4hep::Geometry;
 
-extern TGeoIdentity* DD4hep::Geometry::identityTransform();
+namespace DD4hep  { namespace Geometry  {
+    TGeoIdentity* identityTransform();
+}}
 
 namespace DD4hep  { namespace Geometry  {