diff --git a/requirements.txt b/requirements.txt
index e6ddaf6..46c87d3 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,11 +1,13 @@
 # python 3.8.7
 
 flask==1.1.2
-pdfminer.six==20201018
-pikepdf==2.5.2
 python-socketio==5.2.1
 pyyaml==5.4.1
+lxml==4.6.2
 click==7.1.2
 
+pdfminer.six==20201018
+pikepdf==2.5.2
+
 # NOTE: This is needed for socketio when using the "threading" async mode.
 simple-websocket==0.2.0