diff --git a/.travis.yml b/.travis.yml
index 6692785..5d4454a 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,7 +1,8 @@
+dist: xenial
 language: python
 python:
   - "2.7"
-  - "3.6"
+  - "3.7"
 
 install:
   - pip install --upgrade pip
diff --git a/python/requirements.txt b/python/requirements.txt
index 2d1450b..1db1b72 100644
--- a/python/requirements.txt
+++ b/python/requirements.txt
@@ -1,5 +1,5 @@
 Cython>=0.22
-pystan>=2.14,<=2.18.1
+pystan>=2.14
 numpy>=1.10.0
 pandas>=0.23.4
 matplotlib>=2.0.0