diff --git a/testing/marionette/client/marionette/marionette_test.py b/testing/marionette/client/marionette/marionette_test.py
index 4a4036399fa..585a0a6823c 100644
--- a/testing/marionette/client/marionette/marionette_test.py
+++ b/testing/marionette/client/marionette/marionette_test.py
@@ -153,7 +153,7 @@ class MarionetteJSTestCase(CommonTestCase):
         CommonTestCase.__init__(self, methodName)
 
     @classmethod
-    def add_tests_to_suite(cls, mod_name, filepath, suite, testloader, marionette, testvars):
+    def add_tests_to_suite(cls, mod_name, filepath, suite, testloader, marionette):
         suite.addTest(cls(weakref.ref(marionette), jsFile=filepath))
 
     def runTest(self):