diff --git a/tasks/main.yml b/tasks/main.yml
index a088f7d8878619e80ae4ba30e20af2336829077e..f1e57e8ac1e3744ced79debcdcdfced8a39ed7e0 100644
--- a/tasks/main.yml
+++ b/tasks/main.yml
@@ -77,7 +77,7 @@
       name: nagios
       groups: www-data
       append: true
-  when: inventory_hostname in groups.owncloud_server | union(groups.docker_owncloud) | union(groups.docker_nextcloud)
+  when: inventory_hostname in groups.owncloud_server | default([]) | union(groups.docker_owncloud | default([])) | union(groups.docker_nextcloud | default([]))
 
 - name: Add cron job to update available packages every day
   ansible.builtin.cron: