diff --git a/Dockerfile b/Dockerfile
index a7024ce..74dd892 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -15,7 +15,7 @@ ADD build/*.conf /etc/supervisor/conf.d/
 ADD build/root/*.sh /root/
 
 # get release tag name from build arg
-arg RELEASETAG
+ARG RELEASETAG
 
 # add run bash scripts
 ADD run/nobody/*.sh /home/nobody/