diff --git a/swh/indexer/metadata.py b/swh/indexer/metadata.py
--- a/swh/indexer/metadata.py
+++ b/swh/indexer/metadata.py
@@ -294,6 +294,8 @@
             self.storage.origin_get,
             [{'url': url} for url in origin_urls], ORIGIN_GET_BATCH_SIZE))
         for origin in origins:
+            if origin is None:
+                continue
             head_result = self.origin_head_indexer.index(origin['url'])
             if head_result:
                 origins_with_head.append(origin)
diff --git a/swh/indexer/tests/test_origin_metadata.py b/swh/indexer/tests/test_origin_metadata.py
--- a/swh/indexer/tests/test_origin_metadata.py
+++ b/swh/indexer/tests/test_origin_metadata.py
@@ -237,3 +237,11 @@
     results = list(indexer.idx_storage.origin_intrinsic_metadata_get([
         origin]))
     assert results == []
+
+
+def test_origin_metadata_indexer_unknown_origin(
+        idx_storage, storage, obj_storage):
+
+    indexer = OriginMetadataIndexer(config=REVISION_METADATA_CONFIG)
+    result = indexer.index_list(["https://unknown.org/foo"])
+    assert not result