diff --git a/km3buu/output.py b/km3buu/output.py
index 998f30b689bea87ab7db2d694a67827ea7d1ec5a..df1328e7aa275f5b50758b1138cc3cfdd16b34cd 100644
--- a/km3buu/output.py
+++ b/km3buu/output.py
@@ -102,7 +102,7 @@ EMPTY_KM3NET_HEADER_DICT = {
     "coord_origin": "0 0 0",
     "norma": "0 0",
     "tgen": "0",
-    "simul": ""
+    "simul": "",
     "primary": "0"
 }