diff --git a/sqlite_utils/db.py b/sqlite_utils/db.py
index d849059..ee401b6 100644
--- a/sqlite_utils/db.py
+++ b/sqlite_utils/db.py
@@ -1969,7 +1969,7 @@ class Table(Queryable):
         )
         # Re-add existing indexes
         for index in self.indexes:
-            if index.origin not in ("pk"):
+            if index.origin != "pk":
                 index_sql = self.db.execute(
                     """SELECT sql FROM sqlite_master WHERE type = 'index' AND name = :index_name;""",
                     {"index_name": index.name},
diff --git a/tests/test_transform.py b/tests/test_transform.py
index 7f49afa..42fc88e 100644
--- a/tests/test_transform.py
+++ b/tests/test_transform.py
@@ -551,6 +551,8 @@ def test_transform_strict(fresh_db, strict):
     ],
 )
 def test_transform_indexes(fresh_db, indexes, transform_params):
+    # https://github.com/simonw/sqlite-utils/issues/633
+    # New table should have same indexes as old table after transformation
     dogs = fresh_db["dogs"]
     dogs.insert({"id": 1, "name": "Cleo", "age": 5, "breed": "Labrador"}, pk="id")
 
@@ -617,6 +619,7 @@ def test_transform_retains_indexes_with_foreign_keys(fresh_db):
     ],
 )
 def test_transform_with_indexes_errors(fresh_db, transform_params):
+    # Should error with a compound (name, age) index if age is renamed or dropped
     dogs = fresh_db["dogs"]
     dogs.insert({"id": 1, "name": "Cleo", "age": 5}, pk="id")