diff --git a/environments/common/inventory/group_vars/all/defaults.yml b/environments/common/inventory/group_vars/all/defaults.yml
index 1809d3485..1af2b36e5 100644
--- a/environments/common/inventory/group_vars/all/defaults.yml
+++ b/environments/common/inventory/group_vars/all/defaults.yml
@@ -42,7 +42,7 @@ appliances_local_users_default:
         home: /var/lib/{{ appliances_local_users_ansible_user_name }}
         move_home: true
         local: true
-    
+
     - user: "{{ appliances_local_users_podman }}"
       enable: "{{ 'podman' in group_names }}"
 
@@ -53,7 +53,7 @@ appliances_local_users_default:
         shell: /sbin/nologin
         uid: 202
         system: true
-    
+
     - group:
         name: prometheus
         gid: 976
@@ -64,7 +64,7 @@ appliances_local_users_default:
         shell: /usr/sbin/nologin
         system: true
       enable: "{{ 'prometheus' in group_names }}"
-    
+
     - group:
         name: grafana
         gid: 979
@@ -79,7 +79,7 @@ appliances_local_users_default:
 
 # Overide this to add extra users whilst keeping the defaults.
 appliances_local_users_extra: [] # see format of appliances_local_users_default above
-appliances_local_users: "{{ appliances_local_users_default + appliances_local_users_extra }}"
+appliances_local_users: "{{ (appliances_local_users_default + appliances_local_users_extra) | select | list }}"
 
 ################## bootstrap: extra package installs ######################################
 
@@ -94,7 +94,7 @@ appliances_extra_packages_default:
  - postfix
  - git
  - "{{ 'python36' if ansible_distribution_version == '8.9' else 'python312' }}"
- 
+
 appliances_extra_packages_other: []
-  
-appliances_extra_packages: "{{ appliances_extra_packages_default + appliances_extra_packages_other }}"
+
+appliances_extra_packages: "{{ (appliances_extra_packages_default + appliances_extra_packages_other) | select | list }}"
diff --git a/environments/common/inventory/group_vars/all/openhpc.yml b/environments/common/inventory/group_vars/all/openhpc.yml
index ecaec5663..bcda89b56 100644
--- a/environments/common/inventory/group_vars/all/openhpc.yml
+++ b/environments/common/inventory/group_vars/all/openhpc.yml
@@ -28,7 +28,7 @@ openhpc_packages_default:
   - apptainer
   - podman-compose
 openhpc_packages_extra: []
-openhpc_packages: "{{ openhpc_packages_default + openhpc_packages_extra }}"
+openhpc_packages: "{{ (openhpc_packages_default + openhpc_packages_extra) | select | list }}"
 openhpc_munge_key: "{{ vault_openhpc_mungekey | b64decode }}"
 openhpc_login_only_nodes: login
 openhpc_config_default: