diff --git a/9.10/bullseye/Dockerfile b/9.10/bullseye/Dockerfile
index c6d2178..576541a 100644
--- a/9.10/bullseye/Dockerfile
+++ b/9.10/bullseye/Dockerfile
@@ -1,3 +1,6 @@
+# syntax=docker/dockerfile:1
+# check=error=true
+
 FROM debian:bullseye
 
 ENV LANG C.UTF-8
diff --git a/9.10/slim-bullseye/Dockerfile b/9.10/slim-bullseye/Dockerfile
index 1810f81..43581ef 100644
--- a/9.10/slim-bullseye/Dockerfile
+++ b/9.10/slim-bullseye/Dockerfile
@@ -1,3 +1,6 @@
+# syntax=docker/dockerfile:1
+# check=error=true
+
 FROM debian:bullseye-slim
 
 ENV LANG C.UTF-8
diff --git a/9.6/bullseye/Dockerfile b/9.6/bullseye/Dockerfile
index fe9ad88..ebbe16e 100644
--- a/9.6/bullseye/Dockerfile
+++ b/9.6/bullseye/Dockerfile
@@ -1,3 +1,6 @@
+# syntax=docker/dockerfile:1
+# check=error=true
+
 FROM debian:bullseye
 
 ENV LANG C.UTF-8
diff --git a/9.6/slim-bullseye/Dockerfile b/9.6/slim-bullseye/Dockerfile
index fbd978a..c7673ef 100644
--- a/9.6/slim-bullseye/Dockerfile
+++ b/9.6/slim-bullseye/Dockerfile
@@ -1,3 +1,6 @@
+# syntax=docker/dockerfile:1
+# check=error=true
+
 FROM debian:bullseye-slim
 
 ENV LANG C.UTF-8
diff --git a/9.8/bullseye/Dockerfile b/9.8/bullseye/Dockerfile
index a2f6194..20f9930 100644
--- a/9.8/bullseye/Dockerfile
+++ b/9.8/bullseye/Dockerfile
@@ -1,3 +1,6 @@
+# syntax=docker/dockerfile:1
+# check=error=true
+
 FROM debian:bullseye
 
 ENV LANG C.UTF-8
diff --git a/9.8/slim-bullseye/Dockerfile b/9.8/slim-bullseye/Dockerfile
index 717dd9e..f86746e 100644
--- a/9.8/slim-bullseye/Dockerfile
+++ b/9.8/slim-bullseye/Dockerfile
@@ -1,3 +1,6 @@
+# syntax=docker/dockerfile:1
+# check=error=true
+
 FROM debian:bullseye-slim
 
 ENV LANG C.UTF-8