diff --git a/api/utils/serializer/v1/serializer.py b/api/utils/serializer/v1/serializer.py
index dea48e83..d09a4619 100644
--- a/api/utils/serializer/v1/serializer.py
+++ b/api/utils/serializer/v1/serializer.py
@@ -40,12 +40,20 @@ class AbstractModelAPISerializerV1(AbstractModelAPISerializer):
         else:
             geom = MultiPolygon().geojson
         geo_json = json.loads(geom)
+        ext_ids = list(
+            ExternalIdentifier.objects.filter(
+                internal_id=entry.id
+            ).values_list(
+                "external_id", flat=True
+            )
+        )
         self.properties_data = {
             "id": entry.id,
             "identifier": entry.identifier,
             "title": entry.title,
             "created_on": self._created_on_to_json(entry),
             "modified_on": self._modified_on_to_json(entry),
+            "external_identifiers": ext_ids,
         }
         self._extend_properties_data(entry)
         geo_json["properties"] = self.properties_data