diff --git a/swh/storage/storage.py b/swh/storage/storage.py
--- a/swh/storage/storage.py
+++ b/swh/storage/storage.py
@@ -1234,7 +1234,8 @@
     def metadata_fetcher_add(
         self, fetchers: Iterable[MetadataFetcher], db=None, cur=None
     ) -> None:
-        for (i, fetcher) in enumerate(fetchers):
+        count = 0
+        for fetcher in fetchers:
             if fetcher.metadata is None:
                 raise StorageArgumentException(
                     "MetadataFetcher.metadata may not be None in metadata_fetcher_add."
@@ -1242,7 +1243,8 @@
             db.metadata_fetcher_add(
                 fetcher.name, fetcher.version, dict(fetcher.metadata), cur=cur
             )
-        send_metric("metadata_fetcher:add", count=i + 1, method_name="metadata_fetcher")
+            count += 1
+        send_metric("metadata_fetcher:add", count=count, method_name="metadata_fetcher")
 
     @timed
     @db_transaction(statement_timeout=500)
@@ -1259,7 +1261,8 @@
     def metadata_authority_add(
         self, authorities: Iterable[MetadataAuthority], db=None, cur=None
     ) -> None:
-        for (i, authority) in enumerate(authorities):
+        count = 0
+        for authority in authorities:
             if authority.metadata is None:
                 raise StorageArgumentException(
                     "MetadataAuthority.metadata may not be None in "
@@ -1268,8 +1271,9 @@
             db.metadata_authority_add(
                 authority.type.value, authority.url, dict(authority.metadata), cur=cur
             )
+            count += 1
         send_metric(
-            "metadata_authority:add", count=i + 1, method_name="metadata_authority"
+            "metadata_authority:add", count=count, method_name="metadata_authority"
         )
 
     @timed
diff --git a/swh/storage/tests/test_storage.py b/swh/storage/tests/test_storage.py
--- a/swh/storage/tests/test_storage.py
+++ b/swh/storage/tests/test_storage.py
@@ -3153,6 +3153,13 @@
         res = swh_storage.metadata_fetcher_get(fetcher.name, fetcher.version)
         assert res == fetcher
 
+    def test_metadata_fetcher_add_zero(self, swh_storage, sample_data):
+        fetcher = sample_data.metadata_fetcher
+        actual_fetcher = swh_storage.metadata_fetcher_get(fetcher.name, fetcher.version)
+        assert actual_fetcher is None  # does not exist
+
+        swh_storage.metadata_fetcher_add([])
+
     def test_metadata_authority_add_get(self, swh_storage, sample_data):
         authority = sample_data.metadata_authority
 
@@ -3166,6 +3173,16 @@
         res = swh_storage.metadata_authority_get(authority.type, authority.url)
         assert res == authority
 
+    def test_metadata_authority_add_zero(self, swh_storage, sample_data):
+        authority = sample_data.metadata_authority
+
+        actual_authority = swh_storage.metadata_authority_get(
+            authority.type, authority.url
+        )
+        assert actual_authority is None  # does not exist
+
+        swh_storage.metadata_authority_add([])
+
     def test_content_metadata_add(self, swh_storage, sample_data):
         content = sample_data.content
         fetcher = sample_data.metadata_fetcher