diff --git a/docs/requirements.txt b/docs/requirements.txt
index d0f7e4ad7..1d39ce085 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -4,6 +4,6 @@ Pygments==1.6
 Sphinx==1.2.2
 beautifulsoup4==4.3.2
 docutils==0.12
-lxml==3.3.5
+lxml==4.9.1
 six==1.7.3
 wsgiref==0.1.2