diff --git a/bind/G4Calo.py b/bind/G4Calo.py
index d8f5d4e..de6738c 100644
--- a/bind/G4Calo.py
+++ b/bind/G4Calo.py
@@ -381,7 +381,7 @@ def _fill_event(gd : GeometryDescriptor,
     
     from  G4Calo import __G4System
     G4System = __G4System()
-    G4System.init(gd)
+    G4System.init(gd, 1)
     G4System.run_batch(1, particleSpec, energy, energy,"")
     return gd