diff --git a/ros_buildfarm/templates/ci/ci_job.xml.em b/ros_buildfarm/templates/ci/ci_job.xml.em
index 520e5c9f6..d32c62288 100644
--- a/ros_buildfarm/templates/ci/ci_job.xml.em
+++ b/ros_buildfarm/templates/ci/ci_job.xml.em
@@ -157,7 +157,8 @@ parameters = [
         'sleep 1',
         '',
         '# create a unique dockerfile name prefix',
-        'export DOCKER_IMAGE_PREFIX=$(date +%s.%N)',
+        '[ -z "$EXECUTOR_NUMBER" ] && export EXECUTOR_NUMBER=0',
+        'export DOCKER_IMAGE_PREFIX=executor_$EXECUTOR_NUMBER',
         '',
         '# generate Dockerfile, build and run it',
         '# generating the Dockerfiles for the actual CI tasks',