diff --git a/requirements.txt b/requirements.txt
index 38d53a270..abb84abd6 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,4 +1,5 @@
 docutils>=0.14,<0.19
+jinja2<3.1  # Compatibility with Sphinx 3.5.4.
 libsass==0.18.0
 pygments~=2.6.1
 pygments-csv-lexer~=0.1