diff --git a/sphinx/requirements.txt b/sphinx/requirements.txt
index 1f9f1e6..ee358df 100644
--- a/sphinx/requirements.txt
+++ b/sphinx/requirements.txt
@@ -22,7 +22,7 @@ Jinja2==2.11.3
 joblib==1.0.1
 kiwisolver==1.3.1
 langid==1.1.6
-lxml==4.6.3
+lxml==4.9.1
 MarkupSafe==1.1.1
 matplotlib==3.3.1
 murmurhash==1.0.5