diff --git a/Dockerfile b/Dockerfile
index e043709550..308389163a 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -20,7 +20,8 @@ ENV NODE_ENV=production
 ENV PORT=20128
 ENV HOSTNAME=0.0.0.0
 
-# Runtime writable location for localDb when DATA_DIR is configured to /app/data
+# Data directory inside Docker — must match the volume mount in docker-compose.yml
+ENV DATA_DIR=/app/data
 RUN mkdir -p /app/data
 
 COPY --from=builder /app/public ./public
diff --git a/docker-compose.yml b/docker-compose.yml
index ea3c72f679..0b936ffb08 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -18,6 +18,8 @@
 x-common: &common
   restart: unless-stopped
   env_file: .env
+  environment:
+    - DATA_DIR=/app/data # Must match the volume mount below
   volumes:
     - omniroute-data:/app/data
   healthcheck: