diff --git a/stdlib/3/traceback.pyi b/stdlib/3/traceback.pyi
index de7d74b9c..9d4d2fd9b 100644
--- a/stdlib/3/traceback.pyi
+++ b/stdlib/3/traceback.pyi
@@ -13,5 +13,6 @@ def format_exc(limit: int = ..., chain: bool = ...) -> str: ...
 def extract_stack(f=..., limit=...): ...
 def extract_tb(traceback, limit=...): ...
 def format_list(list): ...
+def format_stack(f=..., limit=...) -> List[str]: ...
 
 # TODO add more