diff --git a/setup.py b/setup.py
index 2138aaa..811bda0 100644
--- a/setup.py
+++ b/setup.py
@@ -21,6 +21,7 @@ setup(name="magic-wormhole-transit-relay",
           "twisted >= 17.5.0",
       ],
       extras_require={
+          ':sys_platform=="win32"': ["twisted[windows]"],
           "dev": ["mock", "tox", "pyflakes"],
       },
       test_suite="wormhole_transit_relay.test",