diff --git a/cool_domain/factory.py b/cool_domain/factory.py
index 47bb0cc..4a91540 100644
--- a/cool_domain/factory.py
+++ b/cool_domain/factory.py
@@ -41,10 +41,10 @@ class Factory:
             msg = "dig is not installed"
             raise FactoryError(msg)
         try:
-            output = subprocess.check_output([dig_bin, domain, "+short"])  # noqa: S603
+            output = subprocess.check_output([dig_bin, domain, "NS", "+short"])  # noqa: S603
             return len(output) == 0
         except subprocess.CalledProcessError:
-            return True
+            return False
 
     def random_domain(self) -> str:
         k = 10000