diff --git a/stdlib/builtins.pyi b/stdlib/builtins.pyi
index 99783cd60..ce2042bca 100644
--- a/stdlib/builtins.pyi
+++ b/stdlib/builtins.pyi
@@ -1477,16 +1477,23 @@ def sorted(
 ) -> list[SupportsRichComparisonT]: ...
 @overload
 def sorted(__iterable: Iterable[_T], *, key: Callable[[_T], SupportsRichComparison], reverse: bool = ...) -> list[_T]: ...
+
+class _SupportsSum(Protocol):
+    def __add__(self, __x: Any) -> Any: ...
+
+_SumT = TypeVar("_SumT", bound=_SupportsSum)
+_SumS = TypeVar("_SumS", bound=_SupportsSum)
+
 @overload
-def sum(__iterable: Iterable[_T]) -> _T | Literal[0]: ...
+def sum(__iterable: Iterable[_SumT]) -> _SumT | Literal[0]: ...
 
 if sys.version_info >= (3, 8):
     @overload
-    def sum(__iterable: Iterable[_T], start: _S) -> _T | _S: ...
+    def sum(__iterable: Iterable[_SumT], start: _SumS) -> _SumT | _SumS: ...
 
 else:
     @overload
-    def sum(__iterable: Iterable[_T], __start: _S) -> _T | _S: ...
+    def sum(__iterable: Iterable[_SumT], __start: _SumS) -> _SumT | _SumS: ...
 
 # The argument to `vars()` has to have a `__dict__` attribute, so can't be annotated with `object`
 # (A "SupportsDunderDict" protocol doesn't work)