diff --git a/ipv6_in_real_life/data_structures.py b/ipv6_in_real_life/data_structures.py
index 3668269..5827c5b 100644
--- a/ipv6_in_real_life/data_structures.py
+++ b/ipv6_in_real_life/data_structures.py
@@ -141,7 +141,7 @@ class Source:
     countries_data: dict[str, CountryData] = dataclasses.field(
         default_factory=dict
     )
-    last_resolved: datetime.datetime | None = None
+    last_resolved: datetime.datetime = datetime.datetime.min
 
     def extend_from_input(
         self, input_entities: Iterable[dict[str, Any]]