diff --git a/docs/rtd-requirements.txt b/docs/rtd-requirements.txt
index f58efbdf..25f53a6d 100644
--- a/docs/rtd-requirements.txt
+++ b/docs/rtd-requirements.txt
@@ -4,3 +4,5 @@ Sphinx==2.3.1
 # mistune 2 and m2r 0.2.1 seem to not play well
 # https://github.com/miyakogi/m2r/issues/66
 mistune<2.0.0
+# Jinja2 imports for sphinx are deprecated over 3.1
+Jinja2<3.1