diff --git a/test/acid.py b/test/acid.py
index d72bbb28..5c4ed2d0 100755
--- a/test/acid.py
+++ b/test/acid.py
@@ -121,8 +121,8 @@ def process_args():
     parser = argparse.ArgumentParser()
     parser.add_argument(
         '--command',
-        default='{} {}'.format(sys.executable,
-                               os.path.join(ROOT_PATH, 'autopep8.py')),
+        default='{0} {1}'.format(sys.executable,
+                                 os.path.join(ROOT_PATH, 'autopep8.py')),
         help='autopep8 command (default: %(default)s)')
     parser.add_argument('--ignore',
                         help='comma-separated errors to ignore',