diff --git a/python/setup.py b/python/setup.py
index 23193cb..f7ee635 100755
--- a/python/setup.py
+++ b/python/setup.py
@@ -146,6 +146,7 @@
     )
     os.environ['PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION'] = 'cpp'
 
+  # Keep this list of dependencies in sync with tox.ini.
   install_requires = ['six', 'setuptools']
   if sys.version_info <= (2,7):
     install_requires.append('ordereddict')