diff --git a/doc/utils/requirements.txt b/doc/utils/requirements.txt
index 1f5711dd6b..6568622f0a 100644
--- a/doc/utils/requirements.txt
+++ b/doc/utils/requirements.txt
@@ -1,4 +1,4 @@
-Sphinx
+Sphinx<6.0.0
 sphinxcontrib-spelling
 git+https://github.com/akohlmey/sphinx-fortran@parallel-read
 sphinx_tabs