diff --git a/Dockerfile b/Dockerfile
index e35694c..ab66c45 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -5,7 +5,7 @@
 #
 # This image will also be used for the YAMLScript track repo's GHA workflows.
 
-FROM ubuntu:24.04
+FROM ubuntu:24.04@sha256:c4a8d5503dfb2a3eb8ab5f807da5bc69a85730fb49b5cfca2330194ebcc41c7b
 
 # Install packages required to run the tests:
 RUN apt-get update \