diff --git a/gprMax/sources.py b/gprMax/sources.py
index 2a890124..c6ffc0aa 100644
--- a/gprMax/sources.py
+++ b/gprMax/sources.py
@@ -107,7 +107,7 @@ class VoltageSource(Source):
             newmaterial = deepcopy(material)
             newmaterial.ID = material.ID + '+VoltageSource_' + str(self.resistance)
             newmaterial.numID = len(G.materials)
-            newmaterial.average = False
+            newmaterial.averagable = False
             newmaterial.type = 'dielectric-smoothed, voltage source'
 
             # Add conductivity of voltage source to underlying conductivity