diff --git a/setup.py b/setup.py
index <HASH>..<HASH> 100644
--- a/setup.py
+++ b/setup.py
@@ -21,6 +21,7 @@ setup(
     install_requires=[
         "fonttools>=3.24.0",
         "attrs>=17.3.0",
+        "lxml",
         "typing ; python_version<'3.5'",
     ],
     classifiers=[
setup.py: require lxml