diff --git a/app.json b/app.json
index 737e5eb0..f3fccb28 100644
--- a/app.json
+++ b/app.json
@@ -49,5 +49,6 @@
     {
       "url": "heroku/python"
     }
-  ]
+  ],
+  "stack": "heroku-18"
 }
\ No newline at end of file