diff --git a/setup.cfg b/setup.cfg
index 18a974f..e2d28ce 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -39,7 +39,7 @@ install_requires =
 [options.extras_require]
 all = boto; brotli; feedgenerator; zopfli; cryptography
 tests = pytest; pytest-cov
-docs = Sphinx; alabaster
+docs = Sphinx; alabaster; cryptography
 
 [options.packages.find]
 exclude =