diff --git a/grizzly/reduce/args.py b/grizzly/reduce/args.py
index a64e6492..8a1da391 100644
--- a/grizzly/reduce/args.py
+++ b/grizzly/reduce/args.py
@@ -123,6 +123,8 @@ def __init__(self):
             "(default: %(default)s).",
         )
 
+        self.parser.add_argument("--test-ext", help="Overwrite testcase file extension")
+
         self.parser.add_argument(
             "--test-index",
             default=[],