diff --git a/bind/G4Calo.py b/bind/G4Calo.py
index ca9cce3..96cd926 100644
--- a/bind/G4Calo.py
+++ b/bind/G4Calo.py
@@ -10,8 +10,8 @@ from IPython.display import Image, display
 class G4System(_G4System):
 
     def run_visualize(self,particleSpec : str, minEnergy_GeV: float, maxEnergy_GeV:float = -1.):
-        if maxEnergy < 0:
-            maxEnergy = minEnergy
+        if maxEnergy_GeV < 0:
+            maxEnergy_GeV = minEnergy_GeV
         _G4System.run_visualize(self, particleSpec, minEnergy_GeV, maxEnergy_GeV)
         self.displayEvent()