diff --git a/Dockerfile b/Dockerfile
index 0ca2248..46ae05b 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,4 +1,4 @@
-FROM alpine
+FROM alpine@sha256:21dc6063fd678b478f57c0e13f47560d0ea4eeba26dfc947b2a4f81f686b9f45
 
 # ca-certificates is needed to download files from S3
 RUN apk update && apk add ca-certificates && rm -rf /var/cache/apk/*