diff --git a/cinderclient/v2/shell.py b/cinderclient/v2/shell.py
index ddf92c2f1..e83548686 100644
--- a/cinderclient/v2/shell.py
+++ b/cinderclient/v2/shell.py
@@ -1060,7 +1060,7 @@ def do_transfer_show(cs, args):
 
 @utils.arg('volume', metavar='<volume>',
            help='Name or ID of the volume to extend.')
-@utils.arg('new-size',
+@utils.arg('new_size',
            metavar='<new_size>',
            type=int,
            help='New size of volume in GB')