diff --git a/rails/3.3/Dockerfile b/rails/3.3/Dockerfile
index b533a32..2a79f6e 100644
--- a/rails/3.3/Dockerfile
+++ b/rails/3.3/Dockerfile
@@ -1,4 +1,4 @@
-FROM ruby:3.3-alpine
+FROM ruby:3.3-alpine@sha256:0bf4169697f44df52cea27b0ceb1a3b715b168625b7c404202e2dfe31dee25e2
 
 # Dependencies
 RUN apk add --no-cache gcompat tzdata shared-mime-info libpq