diff --git a/data/model/tag.py b/data/model/tag.py
index d817fb15d..3cd14f298 100644
--- a/data/model/tag.py
+++ b/data/model/tag.py
@@ -895,7 +895,7 @@ def set_tag_end_ts(tag, end_ts):
   """ Sets the end timestamp for a tag. Should only be called by change_tag_expiration
       or tests.
   """
-  end_ms = end_ts * 1000
+  end_ms = end_ts * 1000 if end_ts is not None else None
 
   with db_transaction():
     # Note: We check not just the ID of the tag but also its lifetime_end_ts, to ensure that it has
diff --git a/data/model/test/test_tag.py b/data/model/test/test_tag.py
index d04ffb96c..731a6d7fe 100644
--- a/data/model/test/test_tag.py
+++ b/data/model/test/test_tag.py
@@ -209,6 +209,13 @@ def test_list_active_tags(initialized_db):
   # Make sure they are returned.
   assert_tags(repository, 'foo', 'bar')
 
+  # Set the expirations to be explicitly empty.
+  set_tag_end_ts(footag, None)
+  set_tag_end_ts(bartag, None)
+
+  # Make sure they are returned.
+  assert_tags(repository, 'foo', 'bar')
+
   # Mark as a tag as expiring in the far future, and make sure it is still returned.
   set_tag_end_ts(footag, footag.lifetime_start_ts + 10000000)