diff --git a/include/ActionInitialization.hh b/include/ActionInitialization.hh
index 158c184..0ceda01 100644
--- a/include/ActionInitialization.hh
+++ b/include/ActionInitialization.hh
@@ -62,6 +62,10 @@ class ActionInitialization : public G4VUserActionInitialization
         G4cout << "ActionInitialization: Setting particle species to " << partSpecies << G4endl;
     }
 
+    void setDetectorConstruction(B4::DetectorConstruction* det){
+      fDetConstruction = det;
+    }
+
   private:
     B4::DetectorConstruction* fDetConstruction = nullptr;
     mutable B4::PrimaryGeneratorAction * gen = nullptr;
diff --git a/src/G4System.cc b/src/G4System.cc
index 9b833e1..fa3b4e4 100644
--- a/src/G4System.cc
+++ b/src/G4System.cc
@@ -36,6 +36,7 @@ void G4System::init(ConstructionWrapper &CW){
 
   // Set mandatory initialization classes
   //
+  
   detConstruction = new B4::DetectorConstruction(&CW);
 
   runManager->SetUserInitialization(detConstruction);
@@ -43,12 +44,13 @@ void G4System::init(ConstructionWrapper &CW){
   if(first_init){
      auto physicsList = new FTFP_BERT;
      runManager->SetUserInitialization(physicsList);
-  
 
-  actionInitialization = new B4a::ActionInitialization(detConstruction);
-  runManager->SetUserInitialization(actionInitialization);
-}
-  if(! first_init){
+    actionInitialization = new B4a::ActionInitialization(detConstruction);
+    runManager->SetUserInitialization(actionInitialization);
+  }
+  else{
+    actionInitialization->setDetectorConstruction(detConstruction);
+
     G4RunManager::GetRunManager()->GeometryHasBeenModified();
     G4RunManager::GetRunManager()->ReinitializeGeometry();
   }
@@ -60,8 +62,8 @@ void G4System::init(ConstructionWrapper &CW){
   // G4VisExecutive can take a verbosity argument - see /vis/verbose guidance.
   // G4VisManager* visManager = new G4VisExecutive("Quiet");
   
-  }
   visManager->Initialize();
+  }
 
   // Get the pointer to the User Interface manager
   UImanager = G4UImanager::GetUIpointer();