diff --git a/stdlib/builtins.pyi b/stdlib/builtins.pyi
index de4813a5d961..385a77520bb9 100644
--- a/stdlib/builtins.pyi
+++ b/stdlib/builtins.pyi
@@ -767,7 +767,7 @@ class list(MutableSequence[_T], Generic[_T]):
     @overload
     def __setitem__(self, s: slice, o: Iterable[_T]) -> None: ...
     def __delitem__(self, i: Union[SupportsIndex, slice]) -> None: ...
-    def __add__(self, x: List[_T]) -> List[_T]: ...
+    def __add__(self, x: List[_T1]) -> List[Union[_T, _T1]]: ...
     def __iadd__(self: _S, x: Iterable[_T]) -> _S: ...
     def __mul__(self, n: int) -> List[_T]: ...
     def __rmul__(self, n: int) -> List[_T]: ...