diff --git a/stacks/dev/.env b/stacks/dev/.env
index e18b988..1877e85 100644
--- a/stacks/dev/.env
+++ b/stacks/dev/.env
@@ -8,6 +8,8 @@ GITEA_DB_PASSWORD=gitea_d3vp4ss_9f2k
 CODE_SERVER_PASSWORD=c0de_s3rver_pass
 
 # BookStack wiki
+# APP_KEY encrypts session data — DO NOT rotate without invalidating sessions.
+BOOKSTACK_APP_KEY=base64:cSR6L4TPEbM2IFi9MyZcnmexvzAlIHAjn/qMzQKO/t4=
 BOOKSTACK_DB_PASSWORD=bookstack_d3v_pass
 BOOKSTACK_DB_ROOT_PASSWORD=bookstack_r00t_pass
 
diff --git a/stacks/dev/docker-compose.yml b/stacks/dev/docker-compose.yml
index baa44c7..14e92d3 100644
--- a/stacks/dev/docker-compose.yml
+++ b/stacks/dev/docker-compose.yml
@@ -118,6 +118,7 @@ services:
       - PGID=1000
       - TZ=${TZ}
       - APP_URL=https://docs.ginnoir.com
+      - APP_KEY=${BOOKSTACK_APP_KEY}
       - DB_HOST=mariadb_bookstack
       - DB_PORT=3306
       - DB_USER=bookstack