diff --git a/plasma/Dockerfile b/plasma/Dockerfile
index e6d750e..cf91711 100644
--- a/plasma/Dockerfile
+++ b/plasma/Dockerfile
@@ -1,9 +1,9 @@
-# syntax = docker/dockerfile:1.2
+# syntax = docker/dockerfile:1
 FROM alpine/base
 USER root
 
 # X session environment variable
-ENV STARTXBIN startplasma-x11
+ENV STARTXBIN=startplasma-x11
 
 # Run
 RUN apk add --no-cache \