diff --git a/app/query_normalisation.py b/app/query_normalisation.py
index f5daa85..595ae21 100644
--- a/app/query_normalisation.py
+++ b/app/query_normalisation.py
@@ -21,10 +21,11 @@ def is_ip_address(query: str) -> bool:
 def resolve_domain_name(domain_name: str) -> ipaddress.IPv4Address | None:
     """Resolve a domain name via DNS or return None."""
     try:
-        ip_address: ipaddress.IPv4Address = ipaddress.IPv4Address(socket.gethostbyname(domain_name))
-    except socket.gaierror:
-        ip_address = None
-    return ip_address
+        result: str = socket.gethostbyname(domain_name)
+        ip_address: ipaddress.IPv4Address = ipaddress.IPv4Address(result)
+        return ip_address
+    except (socket.gaierror, ipaddress.AddressValueError):
+        return None
 
 
 def get_public_ip() -> ipaddress.IPv4Address:
diff --git a/tests/test_ip_info.py b/tests/test_ip_info.py
index 52af7a9..d8901e2 100644
--- a/tests/test_ip_info.py
+++ b/tests/test_ip_info.py
@@ -5,15 +5,15 @@
 import requests_mock
 
 from app.ip_info import (  # pragma: no cover
-    get_ip_information,
     get_autonomous_system_number,
+    get_ip_information,
     get_prefix_information,
 )
 
 
 def test_get_ip_information() -> None:
     """TEST: ensure that the IP information API is working correctly."""
-    test_query = "1.2.3.4"
+    test_query: str = "1.2.3.4"
     ip_info = get_ip_information(test_query)
     assert ip_info.get("status") == "success" and ip_info.get("query") == test_query
 
diff --git a/tests/test_query_normalisation.py b/tests/test_query_normalisation.py
index 569625e..f6183ec 100644
--- a/tests/test_query_normalisation.py
+++ b/tests/test_query_normalisation.py
@@ -31,7 +31,7 @@ def test_resolve_domain_name_true() -> None:
     """TEST: Verifies that DNS resolution is working correctly."""
     domain_name = "one.one.one.one"
     expected_results: list[str] = ["1.1.1.1", "1.0.0.1"]  # Could resolve to either IP
-    assert resolve_domain_name(domain_name) in expected_results
+    assert str(resolve_domain_name(domain_name)) in expected_results
 
 
 def test_resolve_domain_name_false() -> None: