diff --git a/api/utils/serializer/serializer.py b/api/utils/serializer/serializer.py
index f4a35bdc..0af19359 100644
--- a/api/utils/serializer/serializer.py
+++ b/api/utils/serializer/serializer.py
@@ -10,9 +10,11 @@ from abc import abstractmethod
 
 from django.contrib.gis import geos
 from django.contrib.gis.geos import GEOSGeometry
+from django.core.exceptions import ObjectDoesNotExist
 from django.core.paginator import Paginator
 from django.db.models import Q
 
+from api.models import ExternalIdentifier
 from konova.models import Geometry
 from konova.utils.message_templates import DATA_UNSHARED
 
@@ -76,6 +78,14 @@ class AbstractModelAPISerializer:
             del self.lookup["id"]
         else:
             # Return certain object
+            ## But first check, whether this is an external identifier ...
+            try:
+                ## If we can find this _id on our ExternalIdentifier model, we need to map it on the internal id
+                ext_id = ExternalIdentifier.objects.get(external_id=_id)
+                _id = ext_id.internal_id
+            except ObjectDoesNotExist:
+                # If we did not find it, we assume that this is already an internal id. (Or it does not exist at all)
+                pass
             self.lookup["id"] = _id
 
         self.shared_lookup = Q(