diff --git a/stacks/vikunja.yml b/stacks/vikunja.yml
index eb50486..c51ea17 100644
--- a/stacks/vikunja.yml
+++ b/stacks/vikunja.yml
@@ -27,7 +27,7 @@ services:
       replicas: 1
       placement:
         constraints:
-          'node.labels.class.vikunja==true'
+          - 'node.labels.class.vikunja==true'
       labels:
         - 'traefik.enable=true'
         - 'traefik.http.routers.vikunja-api.rule=Host(`todo.rustybever.be`) && PathPrefix(`/api/`, `/dav/`, `/\.well-known/`)'