diff --git a/jobs/dockerfiles.yaml b/jobs/dockerfiles.yaml
index 537ffbd..8a44079 100644
--- a/jobs/dockerfiles.yaml
+++ b/jobs/dockerfiles.yaml
@@ -1,17 +1,18 @@
 - job:
     name: swh-jenkins-dockerfiles
     node: master
     scm:
       - git:
           url: http://forge.softwareheritage.org/source/swh-jenkins-dockerfiles.git
           wipe-workspace: false
     triggers:
-      - pollscm: ""
+      - pollscm:
+          cron: "*/30 * * * *"
       - timed: "0 4 * * *"
     logrotate:
       numToKeep: 50
     wrappers:
       - timestamps
       - ansicolor
     builders:
       - shell: make checkrebuild all