diff --git a/setup.py b/setup.py
index 2279735..fd25fff 100644
--- a/setup.py
+++ b/setup.py
@@ -44,6 +44,7 @@ details = dict(
     keywords="Mode-S ADS-B EHS ELS Comm-B",
     packages=find_packages(exclude=["contrib", "docs", "tests"]),
     install_requires=["numpy", "pyzmq"],
+    extras_require={"fast": ["Cython"]},
     package_data={"pyModeS": ["*.pyx", "*.pxd"]},
     scripts=["pyModeS/streamer/modeslive"],
 )