--- a/testing/vcttesting/mozreview_mach_commands.py
+++ b/testing/vcttesting/mozreview_mach_commands.py
@@ -23,17 +23,17 @@ class MozReviewCommands(object):
     @Command('start', category='mozreview',
         description='Start a MozReview instance')
     @CommandArgument('where', nargs='?',
         help='Directory of MozReview instance')
     @CommandArgument('--bugzilla-port', type=int,
         help='Port Bugzilla HTTP server should listen on.')
     @CommandArgument('--reviewboard-port', type=int,
         help='Port Review Board HTTP server should listen on.')
-    @CommandArgument('--mercurial_port', type=int,
+    @CommandArgument('--mercurial-port', type=int,
         help='Port Mercurial HTTP server should listen on.')
     def start(self, where, bugzilla_port, reviewboard_port,
             mercurial_port):
         mr = self._get_mozreview(where)
         mr.start(bugzilla_port=bugzilla_port,
                 reviewboard_port=reviewboard_port,
                 mercurial_port=mercurial_port,
                 verbose=True)