diff --git a/deploy/docker-compose.yml b/deploy/docker-compose.yml
index e60776e58..b90c1ac33 100644
--- a/deploy/docker-compose.yml
+++ b/deploy/docker-compose.yml
@@ -202,6 +202,15 @@ services:
       nofile:
         soft: 100000
         hard: 100000
+    # Pass the tuning values documented in .env.example to postgres. The
+    # fallbacks are the postgres:18 stock defaults, so nothing changes when
+    # the variables are not set.
+    command: >
+      postgres
+      -c max_connections=${POSTGRES_MAX_CONNECTIONS:-100}
+      -c shared_buffers=${POSTGRES_SHARED_BUFFERS:-128MB}
+      -c effective_cache_size=${POSTGRES_EFFECTIVE_CACHE_SIZE:-4GB}
+      -c maintenance_work_mem=${POSTGRES_MAINTENANCE_WORK_MEM:-64MB}
     volumes:
       - postgres_data:/var/lib/postgresql/data
     environment: