diff --git a/src/python/grpcio_tests/tests_py3_only/interop/xds_interop_client.py b/src/python/grpcio_tests/tests_py3_only/interop/xds_interop_client.py
index d5e994da611..d9634939ea6 100644
--- a/src/python/grpcio_tests/tests_py3_only/interop/xds_interop_client.py
+++ b/src/python/grpcio_tests/tests_py3_only/interop/xds_interop_client.py
@@ -23,6 +23,7 @@ import time
 from typing import (
     DefaultDict,
     Dict,
+    FrozenSet,
     Iterable,
     List,
     Mapping,
@@ -84,7 +85,7 @@ class _StatsWatcher:
     _no_remote_peer: int
     _lock: threading.Lock
     _condition: threading.Condition
-    _metadata_keys: frozenset
+    _metadata_keys: FrozenSet[str]
     _include_all_metadata: bool
     _metadata_by_peer: DefaultDict[
         str, messages_pb2.LoadBalancerStatsResponse.MetadataByPeer