diff --git a/archivebox/index/schema.py b/archivebox/index/schema.py
index 7ed44e74..7508890d 100644
--- a/archivebox/index/schema.py
+++ b/archivebox/index/schema.py
@@ -157,8 +157,7 @@ class Link:
             assert isinstance(self.url, str) and '://' in self.url
             assert self.updated is None or isinstance(self.updated, datetime)
             assert self.title is None or (isinstance(self.title, str) and self.title)
-            #for tag in self.tags.all():
-            #    assert tag is None or isinstance(tag, TaggedItem)
+            assert self.tags is None or isinstance(self.tags, str)
             assert isinstance(self.sources, list)
             assert all(isinstance(source, str) and source for source in self.sources)
             assert isinstance(self.history, dict)