1 files changed, 1 insertions, 1 deletions
diff --git a/event.py b/event.py
index f611edb..a2b99cc 100644
--- a/event.py
+++ b/event.py
@@ -1,7 +1,7 @@
 import numpy as np
 
 class Vertex(object):
-    def __init__(self, particle_name, pos, dir, pol, ke, t0=0.0):
+    def __init__(self, particle_name, pos, dir, ke, t0=0.0, pol=None):
         self.particle_name = particle_name
         self.pos = pos
         self.dir = dir