diff --git a/parsedmarc/resources/maps/base_reverse_dns_map.csv b/parsedmarc/resources/maps/base_reverse_dns_map.csv
index 38333ae..91637b8 100644
--- a/parsedmarc/resources/maps/base_reverse_dns_map.csv
+++ b/parsedmarc/resources/maps/base_reverse_dns_map.csv
@@ -724,7 +724,6 @@ ip-51-89-240.eu,OVH,Web Host
 ip-87-98-138.eu,OVH,Web Host
 ip-92-204-129.us,OVH,Web Host
 ip-92-204-134.us,OVH,Web Host
-ip-92-204-134.us,OVH,Web Host
 iphmx.com,Cisco Cloud Email Security (CES),Email Security
 iphotel.net.br,IPHOTEL Hosped,Web Host
 iphouse.net,Sandwich,Web Host
diff --git a/parsedmarc/resources/maps/find_unknown_base_reverse_dns.py b/parsedmarc/resources/maps/find_unknown_base_reverse_dns.py
index 8a36a86..d2f0055 100755
--- a/parsedmarc/resources/maps/find_unknown_base_reverse_dns.py
+++ b/parsedmarc/resources/maps/find_unknown_base_reverse_dns.py
@@ -24,7 +24,6 @@ def _main():
         if not os.path.exists(file_path):
             print(f"Error: {file_path} does not exist")
         print(f"Loading {file_path}")
-        list_var = []
         with open(file_path) as f:
             for line in f.readlines():
                 domain = line.lower().strip()
@@ -36,6 +35,25 @@ def _main():
 
     load_list(known_unknown_list_file_path, known_unknown_domains)
     load_list(psl_overrides_file_path, psl_overrides)
+    if not os.path.exists(base_reverse_dns_map_file_path):
+        print(f"Error: {base_reverse_dns_map_file_path} does not exist")
+    print(f"Loading {base_reverse_dns_map_file_path}")
+    with open(base_reverse_dns_map_file_path) as f:
+        for row in csv.DictReader(f):
+            domain = row["base_reverse_dns"].lower().strip()
+            if domain in known_domains:
+                print(
+                    f"Error: {domain} is in {base_reverse_dns_map_file_path} multiple times"
+                )
+                exit()
+            else:
+                known_domains.append(domain)
+            if domain in known_unknown_domains and known_domains:
+                print(
+                    f"Error:{domain} is in {known_unknown_list_file_path} and \
+                        {base_reverse_dns_map_file_path}"
+                )
+                exit(1)
     if not os.path.exists(input_csv_file_path):
         print(f"Error: {input_csv_file_path} does not exist")
         exit(1)
diff --git a/parsedmarc/resources/maps/sortlists.py b/parsedmarc/resources/maps/sortlists.py
index 3ba62e7..e914219 100755
--- a/parsedmarc/resources/maps/sortlists.py
+++ b/parsedmarc/resources/maps/sortlists.py
@@ -70,9 +70,9 @@ def sort_csv(
     ) -> None:
         if sort_field_value_must_be_unique:
             if row[sort_field] in seen_sort_field_values:
-                errors.append(f"Line {line_no}: Duplicate row for '{sort_field}'")
+                errors.append(f"Line {line_no}: Duplicate row for '{row[sort_field]}'")
             else:
-                seen_sort_field_values.append(sort_field)
+                seen_sort_field_values.append(row[sort_field])
         for rf in required_fields:
             val = row.get(rf)
             if val is None or val == "":