diff --git a/best_focus.py b/best_focus.py
index 3671e83..95a8fc4 100755
--- a/best_focus.py
+++ b/best_focus.py
@@ -10,7 +10,7 @@ import argparse as ap
 import sys
 
 if __name__ == "__main__":
-    parser = ap.ArgumentParser(prog=sys.argv[1])
+    parser = ap.ArgumentParser(prog=sys.argv[0])
 
     parser.add_argument(
         "files", help="Acquired FITS image filenames of focussing sequence", nargs="*"