diff --git a/docs/reference/buildx_build.md b/docs/reference/buildx_build.md
index b0f6c6ea..ec9112d9 100644
--- a/docs/reference/buildx_build.md
+++ b/docs/reference/buildx_build.md
@@ -129,6 +129,7 @@ $ docker buildx build --build-context project=path/to/project/source .
 ```
 
 ```Dockerfile
+#syntax=docker/dockerfile:1.4
 FROM alpine
 COPY --from=project myfile /
 ```