diff --git a/src/TRestGeant4AnalysisProcess.cxx b/src/TRestGeant4AnalysisProcess.cxx
index 253f6e2..d2e34a7 100644
--- a/src/TRestGeant4AnalysisProcess.cxx
+++ b/src/TRestGeant4AnalysisProcess.cxx
@@ -511,6 +511,8 @@ TRestEvent* TRestGeant4AnalysisProcess::ProcessEvent(TRestEvent* inputEvent) {
     string subEventPrimaryParticleName;
     if (fOutputG4Event->GetSubID() != 0) {
         subEventPrimaryParticleName = fOutputG4Event->GetSubEventPrimaryEventParticleName();
+    } else {
+        subEventPrimaryParticleName = "generator";
     }
     SetObservableValue("subEventPrimaryParticleName", subEventPrimaryParticleName);