diff --git a/master/setup.py b/master/setup.py
index <HASH>..<HASH> 100755
--- a/master/setup.py
+++ b/master/setup.py
@@ -527,7 +527,7 @@ setup_args['extras_require'] = {
     ],
     'docs': [
         'docutils<0.13.0',
-        'sphinx>1.4.0',
+        'sphinx>1.4.0,<2.1.0',
         'sphinxcontrib-blockdiag',
         'sphinxcontrib-spelling',
         'pyenchant',
requirements: Don't update to sphinx <I> or newer