# UNDF: UNDF-2026-000000188
--- a/nova/scheduler/filters/affinity_filter.py
+++ b/nova/scheduler/filters/affinity_filter.py
@@ -143,9 +143,9 @@ class _GroupAffinityFilter(filters.BaseHostFilter):
     def host_passes(self, host_state, spec_obj):
         # Only invoke the filter if 'affinity' is configured
-        policies = (spec_obj.instance_group.policies
-                    if spec_obj.instance_group else [])
+        policies = set(spec_obj.instance_group.policies
+                       if spec_obj.instance_group else [])
         if self.policy_name not in policies:
             return True

-        group_hosts = (spec_obj.instance_group.hosts
-                       if spec_obj.instance_group else [])
+        group_hosts = set(spec_obj.instance_group.hosts
+                          if spec_obj.instance_group else [])
         LOG.debug("Group affinity: check if %(host)s in "
                   "%(configured)s", {'host': host_state.host,
                                      'configured': group_hosts})
         if group_hosts:
             return host_state.host in group_hosts