diff --git a/third_party/2and3/pytz/__init__.pyi b/third_party/2and3/pytz/__init__.pyi
index 20655d1ee..16d57dbb1 100644
--- a/third_party/2and3/pytz/__init__.pyi
+++ b/third_party/2and3/pytz/__init__.pyi
@@ -3,7 +3,7 @@ import datetime
 
 class BaseTzInfo(datetime.tzinfo):
     zone: str = ...
-    def localize(self, dt: datetime.datetime, is_dst: bool = ...) -> datetime.datetime: ...
+    def localize(self, dt: datetime.datetime, is_dst: Optional[bool] = ...) -> datetime.datetime: ...
     def normalize(self, dt: datetime.datetime) -> datetime.datetime: ...
 
 class _UTCclass(BaseTzInfo):