diff --git a/research/karman_reproduce/run.py b/research/karman_reproduce/run.py
index a9905ce..2bc0606 100644
--- a/research/karman_reproduce/run.py
+++ b/research/karman_reproduce/run.py
@@ -56,7 +56,7 @@ def main():
     here = os.path.realpath(os.path.join(os.path.dirname(__file__), "..", ".."))
     if os.path.realpath(args.out).startswith(here):
         raise SystemExit("--out must be outside the checkout")
-    os.makedirs(args.out, exist_ok=True)
+    os.makedirs(args.out)  # fresh directory only; never overwrite results
 
     sys.dont_write_bytecode = True  # import only: write nothing into the DynamisLab tree
     sys.path.insert(0, os.path.join(args.dynamis, "src"))