diff --git a/requirements.txt b/requirements.txt
index 8e1fe6e..c2c8a48 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -9,3 +9,7 @@
 munkres==1.1.2; platform_python_implementation == "PyPy" and python_version >= '3.5'
 zopfli==0.1.6
 fs==2.4.8
+# lxml 4.4.0 breaks OrderedDict attributes in py27 so we pin to previous version
+# https://bugs.launchpad.net/lxml/+bug/1838252
+lxml==4.3.5; python_version < '3.5'  # pyup: ignore
+lxml==4.4.0; python_version >= '3.5'