diff --git a/README.md b/README.md
index a86574c..c787936 100644
--- a/README.md
+++ b/README.md
@@ -112,6 +112,8 @@ Persistent development/production databases record applied-file checksums. Editi
 
 `DATABASE_URL` directs status/validate/migrate at an explicitly supplied persistent database. Otherwise they use `pgstencil_dev`. Schema/type commands always use a disposable migrated clone. Never point template management at a production cluster.
 
+Local services run PostgreSQL 18. The 18 image keeps its data under `/var/lib/postgresql/18/docker` and refuses a volume holding a 17 cluster, so the volume is named `postgres-18-data` and an existing checkout starts a fresh development database. The old volume stays until removed with `docker volume rm <project>_postgres-data`; `docker volume ls` lists it.
+
 ## Resource lifecycle
 
 Each checkout has a Compose project name derived from its absolute path, its own network, and a named Postgres volume. Local credentials and resolved ports are cached in ignored `.pgstencil/services.json`. Both exposed service ports bind to loopback. Change image versions in `compose.yaml`, then stop and restart the services; do not change Postgres major versions against an existing volume without a database upgrade.
diff --git a/compose.yaml b/compose.yaml
index c5fef9d..a680aeb 100644
--- a/compose.yaml
+++ b/compose.yaml
@@ -1,12 +1,12 @@
 services:
   postgres:
-    image: postgres:17.11-alpine
+    image: postgres:18.6-alpine
     environment:
       POSTGRES_USER: pgstencil
       POSTGRES_PASSWORD: pgstencil-local-only
       POSTGRES_DB: postgres
     command: [postgres, -c, max_connections=200]
-    volumes: [postgres-data:/var/lib/postgresql/data]
+    volumes: [postgres-18-data:/var/lib/postgresql]
     ports: ['127.0.0.1::5432']
     healthcheck:
       test: [CMD-SHELL, 'pg_isready -U pgstencil -d postgres']
@@ -27,4 +27,4 @@ services:
         condition: service_healthy
     ports: ['127.0.0.1::5000']
 volumes:
-  postgres-data:
+  postgres-18-data: