--- a/src/twisted/python/test/test_setup.py	2018-09-13 19:23:17.219592749 +0530
+++ b/src/twisted/python/test/test_setup.py	2018-09-13 19:25:02.451597309 +0530
@@ -92,7 +92,7 @@ class OptionalDependenciesTests(TestCase
         The extras need to be parsed with pkg_resources.parse_requirements(),
         which returns a generator.
         """
-        extras = dict(im_an_extra_dependency="thing")
+        extras = dict(im_an_extra_dependency=["thing"])
         attrs = dict(extras_require=extras)
         distribution = Distribution(attrs)