diff --git a/third_party/2and3/flask/wrappers.pyi b/third_party/2and3/flask/wrappers.pyi
index 0dc905945..b60da5ac3 100644
--- a/third_party/2and3/flask/wrappers.pyi
+++ b/third_party/2and3/flask/wrappers.pyi
@@ -31,6 +31,6 @@ class Request(RequestBase, JSONMixin):
     def blueprint(self) -> Optional[str]: ...
 
 class Response(ResponseBase, JSONMixin):
-    default_mimetype: str = ...
+    default_mimetype: Optional[str] = ...
     @property
     def max_cookie_size(self) -> int: ...
diff --git a/third_party/2and3/werkzeug/wrappers.pyi b/third_party/2and3/werkzeug/wrappers.pyi
index ed9a5fb41..1806210b4 100644
--- a/third_party/2and3/werkzeug/wrappers.pyi
+++ b/third_party/2and3/werkzeug/wrappers.pyi
@@ -110,7 +110,7 @@ _SelfT = TypeVar("_SelfT", bound=BaseResponse)
 class BaseResponse:
     charset: str
     default_status: int
-    default_mimetype: str
+    default_mimetype: Optional[str]
     implicit_sequence_conversion: bool
     autocorrect_location_header: bool
     automatically_set_content_length: bool