diff --git a/Dockerfile b/Dockerfile
index 642a553a..577e3089 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,5 +1,5 @@
 ARG IMAGE_VERSION=2019.0.00f0
-ENV IMAGE_TARGET=webgl
+ARG IMAGE_TARGET=webgl
 
 FROM gableroux/unity3d:${IMAGE_VERSION}-${IMAGE_TARGET}