diff --git a/src/G4System.cc b/src/G4System.cc
index 972ebf0..fbb83cc 100644
--- a/src/G4System.cc
+++ b/src/G4System.cc
@@ -9,7 +9,7 @@ void G4System::init(ConstructionWrapper &CW, bool gui){
   //
   runManager =
     G4RunManagerFactory::CreateRunManager(G4RunManagerType::Default);
-  runManager->SetNumberOfThreads(1);
+  runManager->SetNumberOfThreads(20);//more doesn't make sense
 
   G4String session;
   ui = nullptr;