diff --git a/water_sim.py b/water_sim.py
index 31048e5..3839b56 100644
--- a/water_sim.py
+++ b/water_sim.py
@@ -39,7 +39,7 @@ hb_event_list = hb_event * 500
 class Parameters:
     initcon_file: str
     perfect_merging: bool
-    no_merging: bool
+    no_merging: bool = False
 
 
 def main(fn: Path, testrun=False):