diff --git a/check_ns_whois.py b/check_ns_whois.py
index dc32494..d45352d 100755
--- a/check_ns_whois.py
+++ b/check_ns_whois.py
@@ -39,10 +39,10 @@ def get_whois_nsname(zone):
     ns_server = []
     for record in records["name_servers"]:
         if not record.endswith('.'):
-            ns_server.append(f"{record}.")
+            ns_server.append(f"{record.lower()}.")
         else:
-            ns_server.append(f"{record}")
-    return ns_server
+            ns_server.append(f"{record.lower()}")
+    return list(dict.fromkeys(ns_server))
 
 if __name__ == '__main__':