diff --git a/Dockerfile.alpine b/Dockerfile.alpine
index e880bd9..37322c5 100644
--- a/Dockerfile.alpine
+++ b/Dockerfile.alpine
@@ -1,3 +1,4 @@
+# syntax=docker/dockerfile:1
 FROM docker.io/nginxproxy/docker-gen:0.14.5 AS docker-gen
 
 FROM docker.io/nginxproxy/forego:0.18.2 AS forego
diff --git a/Dockerfile.debian b/Dockerfile.debian
index 5c40d25..b7a8372 100644
--- a/Dockerfile.debian
+++ b/Dockerfile.debian
@@ -1,3 +1,4 @@
+# syntax=docker/dockerfile:1
 FROM docker.io/nginxproxy/docker-gen:0.14.5-debian AS docker-gen
 
 FROM docker.io/nginxproxy/forego:0.18.2-debian AS forego
diff --git a/test/requirements/web/Dockerfile b/test/requirements/web/Dockerfile
index da75553..2fb7edf 100644
--- a/test/requirements/web/Dockerfile
+++ b/test/requirements/web/Dockerfile
@@ -1,3 +1,4 @@
+# syntax=docker/dockerfile:1
 # Docker Image running one (or multiple) webservers listening on all given ports from WEB_PORTS environment variable
 
 FROM python:3-alpine