diff --git a/requirements.txt b/requirements.txt
index 1d18dd3..485ba11 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -3,3 +3,6 @@
 # process, which may cause wedges in the gate later.
 
 pbr>=2.0 # Apache-2.0
+
+# xml parsing
+lxml!=3.7.0,>=2.3 # BSD