diff --git a/tasks/main.yaml b/tasks/main.yaml
index b65dc17..e9b3554 100644
--- a/tasks/main.yaml
+++ b/tasks/main.yaml
@@ -14,13 +14,15 @@
       - vars
 
 - name: Verify variables
-  ansible.builtin.include_vars: "{{ lookup('first_found', params) }}"
+  ansible.builtin.include_tasks: "{{ lookup('first_found', params) }}"
   vars:
     params:
       files:
       - "{{ ansible_facts['distribution'] }}_verify_vars.yaml"
       - "{{ ansible_facts['os_family'] }}_verify_vars.yaml"
-      - "verify_vars.yaml"
+      - verify_vars.yaml
+      paths:
+      - tasks
 
 - name: Install sudo
   ansible.builtin.package:
diff --git a/tasks/verify_vars.yaml b/tasks/verify_vars.yaml
index 7ace223..78aa77d 100644
--- a/tasks/verify_vars.yaml
+++ b/tasks/verify_vars.yaml
@@ -1,8 +1,12 @@
 ---
 
-# - name: Verify if not user and group exists for each entry
-#   ansible.builtin.assert:
-#     that:
-#     - (item.user is defined and item.group is not defined) or
-#       (item.user is not defined and item.group is defined)
-#   with_items: "{{ sudo_users_sudoers }}"
+- name: Verify that each entry defines either a user or a group
+  ansible.builtin.assert:
+    that:
+    - (item.user is defined and item.user | length > 0) !=
+      (item.group is defined and item.group | length > 0)
+    fail_msg: >
+      Each entry of sudo_users_sudoers must define either 'user' or 'group',
+      but not both and not none.
+    quiet: true
+  with_items: "{{ sudo_users_sudoers }}"