diff --git a/roles/custom/matrix-element-call/tasks/validate_config.yml b/roles/custom/matrix-element-call/tasks/validate_config.yml
index 86fb84705..dec4027dd 100644
--- a/roles/custom/matrix-element-call/tasks/validate_config.yml
+++ b/roles/custom/matrix-element-call/tasks/validate_config.yml
@@ -17,7 +17,7 @@
   ansible.builtin.fail:
     msg: >
       You need to define a required configuration setting (`{{ item.name }}`).
-  when: "item.when | bool and vars[item.name] | string | length == 0"
+  when: "item.when | bool and lookup('vars', item.name, default='') | string | length == 0"
   with_items:
     - {'name': 'matrix_element_call_container_network', when: true}
     - {'name': 'matrix_element_call_hostname', when: true}