diff --git a/Dockerfile b/Dockerfile
index 8326a32..c2bd0f6 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -9,3 +9,4 @@ COPY html_table_to_markdown.js /var/www
 COPY url_to_markdown_apple_dev_docs.js /var/www
 COPY url_to_markdown_common_filters.js /var/www
 COPY index.js /var/www/
+ENV PORT=1337