diff --git a/requirements_dev.txt b/requirements_dev.txt
index 9409c36..a76fc1f 100644
--- a/requirements_dev.txt
+++ b/requirements_dev.txt
@@ -8,6 +8,6 @@ flake8-expression-complexity
 pep8-naming
 
 #docs
-sphinx<2
+sphinx<4
 recommonmark
 sphinx_rtd_theme