diff --git a/docs/requirements.txt b/docs/requirements.txt
index e2641c8f..b60bca53 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -1,4 +1,6 @@
-sphinx>=2.0
+# sphinx 4.1.x breaks sphinxcontrib-httpdomain which sphinxcontrib-openapi depends on
+# see https://github.com/sphinx-contrib/httpdomain/pull/51
+sphinx>=2.0,<4.1
 reno>=2.2
 sphinx_rtd_theme~=0.5.0
 jinja2~=2.11.2