diff --git a/third_party/2/gflags.pyi b/third_party/2/gflags.pyi
index cdec93a95..4242e040b 100644
--- a/third_party/2/gflags.pyi
+++ b/third_party/2/gflags.pyi
@@ -1,4 +1,4 @@
-from typing import Any, Callable, Dict, Iterable, IO, List, Union
+from typing import Any, Callable, Dict, Iterable, IO, List, Optional, Union
 from types import ModuleType
 
 class FlagsError(Exception): ...
@@ -114,7 +114,7 @@ def DEFINE(parser: ArgumentParser, name: str, default: Any, help: str,
 def DEFINE_flag(flag: Flag, flag_values: FlagValues = ...) -> None: ...
 def DECLARE_key_flag(flag_name: str, flag_values: FlagValues = ...) -> None: ...
 def ADOPT_module_key_flags(module: ModuleType, flag_values: FlagValues = ...) -> None: ...
-def DEFINE_string(name: str, default: str, help: str, flag_values: FlagValues = ..., **args: Any): ...
+def DEFINE_string(name: str, default: Optional[str], help: str, flag_values: FlagValues = ..., **args: Any): ...
 
 class BooleanParser(ArgumentParser):
     def Convert(self, argument: Any) -> bool: ...