diff --git a/k4Interface/include/k4Interface/IGeoSvc.h b/k4Interface/include/k4Interface/IGeoSvc.h
index d17e2189..422851aa 100644
--- a/k4Interface/include/k4Interface/IGeoSvc.h
+++ b/k4Interface/include/k4Interface/IGeoSvc.h
@@ -32,9 +32,10 @@ class G4VUserDetectorConstruction;
 class GAUDI_API IGeoSvc : virtual public IService {
 public:
   DeclareInterfaceID(IGeoSvc, 1, 0);
-  virtual dd4hep::DetElement           getDD4HepGeo() = 0;
-  virtual dd4hep::Detector*            lcdd()         = 0;
-  virtual G4VUserDetectorConstruction* getGeant4Geo() = 0;
+  virtual dd4hep::DetElement           getDD4HepGeo()                            = 0;
+  virtual dd4hep::Detector*            lcdd()                                    = 0;
+  virtual G4VUserDetectorConstruction* getGeant4Geo()                            = 0;
+  virtual std::string                  constantAsString(std::string const& name) = 0;
   virtual ~IGeoSvc() {}
 };