diff --git a/app.json b/app.json
index b62002e..d2386b7 100644
--- a/app.json
+++ b/app.json
@@ -22,6 +22,10 @@
         "heroku-postgresql"
     ],
     "env": {
+        "APP_KEY": {
+            "description": "Used for the auth system.",
+            "generator": "secret"
+        },
         "APP_TIMEZONE": {
             "description": "Application time zone.",
             "value": "Etc/UTC"