diff --git a/Dockerfile b/Dockerfile
index 41f011e..1bc226b 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -7,7 +7,7 @@ ADD timezone /etc/timezone
 ADD run.sh /usr/local/bin/
 
 
-ARG DATABASE_URL = 'db:5432'
+ARG DATABASE_URL='db:5432'
 
 ENV DATABASE_URL=${DATABASE_URL}