diff --git a/requirements-dev.txt b/requirements-dev.txt
index be90c87..83dc34e 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -3,6 +3,7 @@
 flake8 ~= 3.6
 flake8-colors
 flake8-docstrings
+lxml ~= 4.4.1
 mypy ~= 0.701
 pep8-naming
 pylint ~= 2.1