diff -Nur a/setup.py b/setup.py
--- a/setup.py	2019-12-09 00:36:58.000000000 +0800
+++ b/setup.py	2022-08-16 14:05:40.513781439 +0800
@@ -2,7 +2,7 @@
 
 from setuptools import setup, find_packages
 
-requires = ['blockdiag>=1.5.0', 'actdiag>=0.5.3', 'Sphinx>=2.0']
+requires = ['blockdiag>=1.5.0', 'actdiag>=0.5.3', 'Sphinx>=1.8']
 
 setup(
     name='sphinxcontrib-actdiag',