diff --git a/setup.py b/setup.py
index 7e7a587..5d2c76c 100644
--- a/setup.py
+++ b/setup.py
@@ -29,7 +29,9 @@ setup(name="magic-wormhole",
                         "autobahn[twisted] >= 0.14.1",
                         "hkdf", "tqdm",
                         ],
-      extras_require={"tor": ["txtorcon", "ipaddress"]},
+      extras_require={"tor": ["txtorcon", "ipaddress"],
+                      "windows": ["pypiwin32"]
+                      },
       test_suite="wormhole.test",
       cmdclass=commands,
       )