diff --git a/app/Dockerfile b/app/Dockerfile
index dc3de69..6fabda3 100644
--- a/app/Dockerfile
+++ b/app/Dockerfile
@@ -1,4 +1,4 @@
-FROM alpine:3.9
+FROM alpine:3.20@sha256:d9e853e87e55526f6b2917df91a2115c36dd7c696a35be12163d44e6e2a4b6bc
 ADD app /
 ADD index.html.tmpl /
 EXPOSE 80