diff --git a/docs/requirements.txt b/docs/requirements.txt
index 156c38a..c8c040b 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -18,7 +18,7 @@ joblib==0.16.0; python_version > "2.7"
 limits==1.5.1
 livereload==2.6.3
 lunr==0.5.8
-lxml==4.6.5
+lxml==4.9.1
 markdown==3.2.2
 markupsafe==1.1.1
 mkautodoc==0.1.0