diff --git a/requirements.txt b/requirements.txt
index 4f967cc..8bb14d0 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -3,4 +3,5 @@ mkdocs-material==7.3.6
 mkdocs-git-revision-date-localized-plugin
 mkdocs-git-committers-plugin-2
 mkdocs-git-authors-plugin
+lxml
 invoke