diff --git a/aiplan/requirements.txt b/aiplan/requirements.txt
index efcad4d..8196256 100644
--- a/aiplan/requirements.txt
+++ b/aiplan/requirements.txt
@@ -27,7 +27,7 @@ gunicorn==19.1.1
 ipdb==0.8
 ipython==2.3.0
 jsonfield==1.0.0
-lxml==3.4.0
+lxml==4.9.1
 matplotlib==1.4.0
 mock==1.0.1
 networkx==1.9.1