diff --git a/requirements.txt b/requirements.txt
index b8d5955..9115bba 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -14,7 +14,7 @@ idna==2.5
 incremental==16.10.1
 ipython==5.3.0
 ipython-genutils==0.2.0
-lxml==3.7.3
+lxml==4.9.1
 matplotlib==2.0.0
 numpy==1.12.1
 packaging==16.8