diff --git a/requirements.txt b/requirements.txt
index a4f6f83f8..0973685ee 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,7 +1,7 @@
 gym==0.14.0
 numpy==1.18.4
 scipy==1.1.0
-lxml==4.4.1
+lxml==4.9.1
 pyprind==2.11.2
 nose2==0.8.0
 six==1.11.0