diff --git a/Simulation/G4Extensions/ExtraParticles/src/CustomParticle.cxx b/Simulation/G4Extensions/ExtraParticles/src/CustomParticle.cxx
index f4757dc6b99a297db68b5f807bc676be799112a1..0e855a55f75dbe234390c7e58012a2410049bf98 100644
--- a/Simulation/G4Extensions/ExtraParticles/src/CustomParticle.cxx
+++ b/Simulation/G4Extensions/ExtraParticles/src/CustomParticle.cxx
@@ -1,5 +1,5 @@
 /*
-  Copyright (C) 2002-2019 CERN for the benefit of the ATLAS collaboration
+  Copyright (C) 2002-2022 CERN for the benefit of the ATLAS collaboration
 */
 
 #include "CustomParticle.hh"
@@ -8,6 +8,8 @@
 // ###                           CustomParticle                       ###
 // ######################################################################
 
+using namespace ExtraParticles;
+
 CustomParticle::CustomParticle(const G4String &name, G4double mass,
                                G4double width, G4int charge, G4int pdg,
                                G4bool stable, G4double lifetime)
diff --git a/Simulation/G4Extensions/ExtraParticles/src/CustomParticle.hh b/Simulation/G4Extensions/ExtraParticles/src/CustomParticle.hh
index a1022df124f349fcd148c6a0e9f448e3b5093535..c47b8b73b2262a13fbd80ffff00e164126e1ca84 100644
--- a/Simulation/G4Extensions/ExtraParticles/src/CustomParticle.hh
+++ b/Simulation/G4Extensions/ExtraParticles/src/CustomParticle.hh
@@ -1,5 +1,5 @@
 /*
-  Copyright (C) 2002-2019 CERN for the benefit of the ATLAS collaboration
+  Copyright (C) 2002-2022 CERN for the benefit of the ATLAS collaboration
 */
 
 #ifndef EXTRA_PARTICLES__CUSTOM_PARTICLE_H
@@ -12,6 +12,8 @@
 // ###                           CustomParticle                       ###
 // ######################################################################
 
+namespace ExtraParticles {
+
 class CustomParticle : public G4ParticleDefinition {
 
   public:
@@ -21,4 +23,6 @@ class CustomParticle : public G4ParticleDefinition {
     virtual ~CustomParticle() {}
 };
 
+} // namespace ExtraParticles
+
 #endif // EXTRA_PARTICLES__CUSTOM_PARTICLE_H
diff --git a/Simulation/G4Extensions/ExtraParticles/src/ExtraParticlesPhysicsTool.cxx b/Simulation/G4Extensions/ExtraParticles/src/ExtraParticlesPhysicsTool.cxx
index 2e8e0ce18f7a534a805d83f093f71fdfeafc689f..db235317b9333668d1bb178c564231cd82076362 100644
--- a/Simulation/G4Extensions/ExtraParticles/src/ExtraParticlesPhysicsTool.cxx
+++ b/Simulation/G4Extensions/ExtraParticles/src/ExtraParticlesPhysicsTool.cxx
@@ -1,5 +1,5 @@
 /*
-  Copyright (C) 2002-2019 CERN for the benefit of the ATLAS collaboration
+  Copyright (C) 2002-2022 CERN for the benefit of the ATLAS collaboration
 */
 
 // Include files
@@ -17,6 +17,8 @@
 #include "G4hIonisation.hh"
 #include "G4hMultipleScattering.hh"
 
+using namespace ExtraParticles;
+
 //-----------------------------------------------------------------------------
 // Implementation file for class : ExtraParticlesPhysicsTool
 //