diff --git a/docker/Dockerfile b/docker/Dockerfile
index 5500673..fb564b2 100644
--- a/docker/Dockerfile
+++ b/docker/Dockerfile
@@ -1,7 +1,7 @@
 FROM ubuntu:24.04 AS base
 
 SHELL ["/bin/sh", "-x", "-c"]
-ENV SERIAL 2
+ENV SERIAL=2
 
 ########################################
 FROM base AS builder