diff --git a/requirements.txt b/requirements.txt
index 7b721d0..5dae3d2 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,3 +1,4 @@
 click==6.7
 python-dateutil==2.5.1
 requests>=2.20.0
+sortedcontainers>=2.4