diff --git a/macro/run_simScript.py b/macro/run_simScript.py
index 180e7e37c..fb11e3230 100755
--- a/macro/run_simScript.py
+++ b/macro/run_simScript.py
@@ -148,7 +148,7 @@
     help="Set Decay Volume medium to vacuum(vessel structure changes)",
     action="store_const",
     const="vacuums",
-    default="helium",
+    default="helium"
 )
 parser.add_argument("--SND", dest="SND", help="Activate SND.", action='store_true')
 parser.add_argument("--noSND", dest="SND", help="Deactivate SND. NOOP, as it currently defaults to off.", action='store_false')