diff --git a/Dockerfile b/Dockerfile
index 3ba12ff..57bd7f4 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -6,6 +6,7 @@ WORKDIR /
 
 # The environment port to expose. 
 ENV PORT=9090
+EXPOSE 9090
 
 # The JAR file path. 
 # ARG JAR_FILE=*.jar