diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 2203a4957f75e60f586122ce8f92db4d7ec2b068..58939e3cd0702fa0dbeac93b9dd9481cb39c93e8 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -20,7 +20,7 @@ deploy ubuntu:
   script:
     - image_name="${CI_REGISTRY}/${CI_PROJECT_PATH,,}"
     - podman push "${image_name}/ubuntu"
-    - calver="$(date +'%Y-%m-%dT%H:%M')"
+    - calver="$(date -u +'%Y%m%dT%H%MZ')"
     - podman tag "${image_name}/jupyterhub" "${image_name}/jupyterhub:$calver"
     - podman push "${image_name}/jupyterhub:$calver"
     - podman image rm "${image_name}/jupyterhub:$calver"