diff --git a/python/requirements.txt b/python/requirements.txt
index f85562c..5cdc363 100644
--- a/python/requirements.txt
+++ b/python/requirements.txt
@@ -1,6 +1,6 @@
 Cython>=0.22
 cmdstanpy==0.9.68
-pystan>=2.14
+pystan~=2.19.1.1
 numpy>=1.15.4
 pandas>=1.0.4
 matplotlib>=2.0.0