diff --git a/octodns/processor/arpa.py b/octodns/processor/arpa.py
index 1e121eb..7df1d1e 100644
--- a/octodns/processor/arpa.py
+++ b/octodns/processor/arpa.py
@@ -41,8 +41,6 @@ class AutoArpa(BaseProcessor):
                     ptr = ip_address(ip).reverse_pointer
                     auto_arpa_priority = record.octodns.get('auto_arpa_priority', 999)
                     self._records[f'{ptr}.'].append((auto_arpa_priority, record.fqdn))
-                    unique_list = list(set(self._records[f'{ptr}.']))
-                    self._records[f'{ptr}.'] = unique_list
 
         return desired
 
@@ -61,6 +59,7 @@ class AutoArpa(BaseProcessor):
         for arpa, fqdns in self._records.items():
             if arpa.endswith(f'.{zone_name}'):
                 name = arpa[:-n]
+                fqdns = list(set(fqdns))
                 fqdns = sorted(fqdns)
                 fqdns = [d[1] for d in fqdns]
                 fqdns = fqdns[:self.max_auto_arpa]
diff --git a/tests/test_octodns_processor_arpa.py b/tests/test_octodns_processor_arpa.py
index 124ca0a..7152857 100644
--- a/tests/test_octodns_processor_arpa.py
+++ b/tests/test_octodns_processor_arpa.py
@@ -165,6 +165,7 @@ class TestAutoArpa(TestCase):
         zone.add_record(record)
         aa = AutoArpa('auto-arpa')
         aa.process_source_zone(zone, [])
+        aa._records = list(set(aa._records))
         self.assertEqual(
             {
                 '4.3.2.1.in-addr.arpa.': [(999, 'dynamic.unit.tests.')],