diff --git a/docs/requirements.txt b/docs/requirements.txt
index 512fae8..233ad92 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -9,7 +9,7 @@ chardet==3.0.4
 cycler==0.10.0
 idna==2.10
 kiwisolver==1.2.0
-lxml==4.6.3
+lxml==4.9.1
 matplotlib==3.3.2
 multidict==4.7.6
 multitasking==0.0.9