diff --git a/requirements.txt b/requirements.txt
index d66230d..0aeb579 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -30,3 +30,4 @@ elasticsearch>=5.0.0,<6.0.0
 apscheduler # MIT License
 paste>=3.0.2
 webob>=1.8.5
+lxml>=4.4.0