diff --git a/php/Dockerfile b/php/Dockerfile
index 5a39f35..0396364 100644
--- a/php/Dockerfile
+++ b/php/Dockerfile
@@ -1,4 +1,4 @@
-# syntax=docker/dockerfile:1.6
+# syntax=docker/dockerfile:1.9
 
 ARG ALPINE_VERSION
 ARG PHP_SHORT_VERSION