diff --git a/Dockerfile b/Dockerfile
index 7de70fa..5d353bf 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -17,9 +17,10 @@ RUN yarn --production --pure-lockfile \
 
 # Expose port 4002
 EXPOSE 4002
+ENV PORT=4002
 
 # Setting run-command, using explicit `node` command
 # rather than `yarn` or `npm` to use less memory
 # https://github.com/nolanlawson/pinafore/issues/971
-CMD ["PORT=4002", "node", "server.js"]
+CMD ["node", "server.js"]