diff --git a/requirements.txt b/requirements.txt
index 35ef8f614..e4f0c3048 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -8,6 +8,7 @@ Pygments==2.0.2
 py-gfm==0.1.2
 blinker==1.4
 monotonic==0.3
+lxml==3.6.0
 pyexcel==0.2.1
 pyexcel-io==0.1.0
 pyexcel-xls==0.1.0