diff --git a/docs/environment-docs.yml b/docs/environment-docs.yml
index 07b8ac9d..7d9c9756 100644
--- a/docs/environment-docs.yml
+++ b/docs/environment-docs.yml
@@ -35,7 +35,7 @@ dependencies:
   - setuptools_scm
 
   # Documentation
-  - sphinx
+  - sphinx<4.0
   - sphinx_rtd_theme
   - sphinx-click
   - IPython