diff --git a/swh/journal/serializers.py b/swh/journal/serializers.py
--- a/swh/journal/serializers.py
+++ b/swh/journal/serializers.py
@@ -49,6 +49,7 @@
 
 
 def object_key(object_type: str, object_) -> KeyType:
+    object_type = object_type.split(":", 1)[0]
     if object_type in ("revision", "release", "directory", "snapshot"):
         return object_.id
     elif object_type == "content":
diff --git a/swh/journal/tests/test_serializers.py b/swh/journal/tests/test_serializers.py
--- a/swh/journal/tests/test_serializers.py
+++ b/swh/journal/tests/test_serializers.py
@@ -8,6 +8,8 @@
 from collections import OrderedDict
 from typing import Iterable
 
+import pytest
+
 from swh.journal import serializers
 
 from .conftest import TEST_OBJECTS
@@ -35,7 +37,15 @@
     """Test whether get_key works on all our objects"""
     for object_type, objects in TEST_OBJECTS.items():
         for obj in objects:
-            assert serializers.object_key(object_type, obj) is not None
+            key = serializers.object_key(object_type, obj)
+            assert key is not None
+            # also test "flags" are ignored
+            assert key == serializers.object_key(f"{object_type}:", obj)
+            assert key == serializers.object_key(f"{object_type}:toto", obj)
+            assert key == serializers.object_key(f"{object_type}:toto:tutu", obj)
+
+            with pytest.raises(ValueError):
+                serializers.object_key(f"{object_type};toto", obj)
 
 
 def test_pprint_key():