diff --git a/python/requirements.txt b/python/requirements.txt
index 86aa7ae..cb4426f 100644
--- a/python/requirements.txt
+++ b/python/requirements.txt
@@ -1,9 +1,9 @@
 Cython>=0.22
-pystan>=2.14
+pystan>=2.14,<=2.18.1
 numpy>=1.10.0
 pandas>=0.20.1
 matplotlib>=2.0.0
 lunardate>=0.1.5
 convertdate>=2.1.2
 holidays>=0.9.5
-setuptools-git>=1.2
\ No newline at end of file
+setuptools-git>=1.2