diff --git a/swh/storage/fixer.py b/swh/storage/fixer.py
--- a/swh/storage/fixer.py
+++ b/swh/storage/fixer.py
@@ -8,8 +8,7 @@
 import logging
 from typing import Any, Dict, List, Optional
 
-from swh.model.identifiers import normalize_timestamp
-from swh.model.model import Origin
+from swh.model.model import Origin, TimestampWithTimezone
 
 logger = logging.getLogger(__name__)
 
@@ -70,12 +69,12 @@
     """
     if date is None:
         return True
-    date = normalize_timestamp(date)
-    return (
-        (-(2 ** 63) <= date["timestamp"]["seconds"] < 2 ** 63)
-        and (0 <= date["timestamp"]["microseconds"] < 10 ** 6)
-        and (-(2 ** 15) <= date["offset"] < 2 ** 15)
-    )
+    try:
+        TimestampWithTimezone.from_dict(date)
+    except ValueError:
+        return False
+    else:
+        return True
 
 
 def _check_revision_date(rev):
diff --git a/swh/storage/tests/algos/test_diff.py b/swh/storage/tests/algos/test_diff.py
--- a/swh/storage/tests/algos/test_diff.py
+++ b/swh/storage/tests/algos/test_diff.py
@@ -11,7 +11,6 @@
 import pytest
 
 from swh.model.hashutil import hash_to_bytes
-from swh.model.identifiers import directory_identifier
 from swh.storage.algos import diff
 
 from .test_dir_iterator import DirectoryModel
diff --git a/swh/storage/tests/algos/test_dir_iterator.py b/swh/storage/tests/algos/test_dir_iterator.py
--- a/swh/storage/tests/algos/test_dir_iterator.py
+++ b/swh/storage/tests/algos/test_dir_iterator.py
@@ -8,7 +8,7 @@
 
 from swh.model.from_disk import DentryPerms
 from swh.model.hashutil import MultiHash, hash_to_bytes
-from swh.model.identifiers import directory_identifier
+from swh.model.model import Directory
 from swh.storage.algos.dir_iterators import dir_iterator
 
 # flake8: noqa
@@ -30,7 +30,19 @@
 
     def __getitem__(self, item):
         if item == "target":
-            return hash_to_bytes(directory_identifier(self))
+            return Directory.from_dict(
+                {
+                    "entries": [
+                        {
+                            "name": entry["name"],
+                            "target": entry["target"],
+                            "type": entry["type"],
+                            "perms": entry["perms"],
+                        }
+                        for entry in self.data["entries"]
+                    ]
+                }
+            ).id
         else:
             return self.data[item]