diff --git a/requirements.txt b/requirements.txt
index 9f7a7a69900daa9f8b668162cf91cef76d176010..f0eb1a8ce16d8c0379a290a65185f27318e0bbe7 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -6,6 +6,7 @@ PyYAML
 shapely
 scipy
 terminaltables
+Cython
 pycocotools
 #xtcocotools==1.6 #only for crowdpose
 setuptools>=42.0.0