diff --git a/Dockerfile b/Dockerfile
index 1cba586..9abfc03 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,4 +1,4 @@
-# syntax=docker/dockerfile:1.20.0
+# syntax=docker/dockerfile:1.21.0
 FROM koalaman/shellcheck-alpine:v0.11.0 AS shellcheck
 WORKDIR /src
 RUN --mount=type=bind,target=. \