diff --git a/Dockerfile b/Dockerfile
index 4675432..111b50e 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,7 +1,7 @@
 FROM debian:stretch
 EXPOSE 34197/udp
 
-ARG FACTORIO_VERSION 0.17.79
+ARG FACTORIO_VERSION=0.17.79
 
 ADD bin/entrypoint.sh /entrypoint.sh