diff --git a/swh/indexer/storage/__init__.py b/swh/indexer/storage/__init__.py
--- a/swh/indexer/storage/__init__.py
+++ b/swh/indexer/storage/__init__.py
@@ -49,6 +49,21 @@
 }
 
 
+def sanitize_json(doc):
+    """Recursively replaces NUL characters, as postgresql does not allow
+    them in text fields."""
+    if isinstance(doc, str):
+        return doc.replace("\x00", "")
+    elif not hasattr(doc, "__iter__"):
+        return doc
+    elif isinstance(doc, dict):
+        return {sanitize_json(k): sanitize_json(v) for (k, v) in doc.items()}
+    elif isinstance(doc, (list, tuple)):
+        return [sanitize_json(v) for v in doc]
+    else:
+        raise TypeError(f"Unexpected object type in sanitize_json: {doc}")
+
+
 def get_indexer_storage(cls: str, **kwargs) -> IndexerStorageInterface:
     """Instantiate an indexer storage implementation of class `cls` with arguments
     `kwargs`.
@@ -397,8 +412,12 @@
 
         db.mktemp_content_metadata(cur)
 
+        rows = [m.to_dict() for m in metadata]
+        for row in rows:
+            row["metadata"] = sanitize_json(row["metadata"])
+
         db.copy_to(
-            [m.to_dict() for m in metadata],
+            rows,
             "tmp_content_metadata",
             ["id", "metadata", "indexer_configuration_id"],
             cur,
@@ -447,8 +466,12 @@
 
         db.mktemp_directory_intrinsic_metadata(cur)
 
+        rows = [m.to_dict() for m in metadata]
+        for row in rows:
+            row["metadata"] = sanitize_json(row["metadata"])
+
         db.copy_to(
-            [m.to_dict() for m in metadata],
+            rows,
             "tmp_directory_intrinsic_metadata",
             ["id", "metadata", "mappings", "indexer_configuration_id"],
             cur,
@@ -487,8 +510,12 @@
 
         db.mktemp_origin_intrinsic_metadata(cur)
 
+        rows = [m.to_dict() for m in metadata]
+        for row in rows:
+            row["metadata"] = sanitize_json(row["metadata"])
+
         db.copy_to(
-            [m.to_dict() for m in metadata],
+            rows,
             "tmp_origin_intrinsic_metadata",
             [
                 "id",
@@ -625,8 +652,12 @@
 
         db.mktemp_origin_extrinsic_metadata(cur)
 
+        rows = [m.to_dict() for m in metadata]
+        for row in rows:
+            row["metadata"] = sanitize_json(row["metadata"])
+
         db.copy_to(
-            [m.to_dict() for m in metadata],
+            rows,
             "tmp_origin_extrinsic_metadata",
             [
                 "id",
diff --git a/swh/indexer/tests/storage/test_storage.py b/swh/indexer/tests/storage/test_storage.py
--- a/swh/indexer/tests/storage/test_storage.py
+++ b/swh/indexer/tests/storage/test_storage.py
@@ -526,6 +526,60 @@
     ]
     row_class = ContentMetadataRow
 
+    def test_add_with_null(
+        self, swh_indexer_storage_with_data: Tuple[IndexerStorageInterface, Any]
+    ) -> None:
+        storage, data = swh_indexer_storage_with_data
+        etype = self.endpoint_type
+        tool = data.tools[self.tool_name]
+
+        # conftest fills it with mimetypes
+        storage.journal_writer.journal.objects = []  # type: ignore
+
+        query = [data.sha1_2, data.sha1_1]
+        data1 = self.row_class.from_dict(
+            {
+                "id": data.sha1_2,
+                "metadata": {"description": "with\u0000nul"},
+                "indexer_configuration_id": tool["id"],
+            }
+        )
+
+        # when
+        summary = endpoint(storage, etype, "add")([data1])
+        assert summary == expected_summary(1, etype)
+
+        # then
+        actual_data = list(endpoint(storage, etype, "get")(query))
+
+        # then
+        expected_data_postgresql = [
+            self.row_class.from_dict(
+                {
+                    "id": data.sha1_2,
+                    "metadata": {"description": "withnul"},
+                    "tool": tool,
+                }
+            )
+        ]
+        expected_data_verbatim = [
+            self.row_class.from_dict(
+                {
+                    "id": data.sha1_2,
+                    "metadata": {"description": "with\u0000nul"},
+                    "tool": tool,
+                }
+            )
+        ]
+
+        assert actual_data in (expected_data_postgresql, expected_data_verbatim)
+
+        journal_objects = storage.journal_writer.journal.objects  # type: ignore
+        actual_journal_data = [
+            obj for (obj_type, obj) in journal_objects if obj_type == self.endpoint_type
+        ]
+        assert list(sorted(actual_journal_data)) == list(sorted(expected_data_verbatim))
+
 
 class TestIndexerStorageDirectoryIntrinsicMetadata(StorageETypeTester):
     """Test Indexer Storage directory_intrinsic_metadata related methods"""