diff --git a/Dockerfile.jenkins b/Dockerfile.jenkins
index 7928040..6f35268 100644
--- a/Dockerfile.jenkins
+++ b/Dockerfile.jenkins
@@ -1,4 +1,5 @@
 FROM schemers/chibi:head
 RUN apt-get update && apt-get install -y \
     gcc ca-certificates libffi-dev docker.io make
-RUN snow-chibi install --impls=chibi --always-yes retropikzel.test-r7rs
+ARG timestamp=0
+RUN snow-chibi install --impls=chibi --always-yes retropikzel.test-r7rs && echo "${timestamp}"
diff --git a/Jenkinsfile b/Jenkinsfile
index d8f2a73..62b2d88 100644
--- a/Jenkinsfile
+++ b/Jenkinsfile
@@ -4,6 +4,7 @@ pipeline {
             label 'docker-x86_64'
             filename 'Dockerfile.jenkins'
             args '--user=root --privileged -v /var/run/docker.sock:/var/run/docker.sock'
+            additionalBuildArgs "--build-arg timestamp=${currentBuild.startTimeInMillis}"
             reuseNode true
         }
     }