diff --git a/stdlib/2/heapq.pyi b/stdlib/2/heapq.pyi
index d76aac49e..5c56a0710 100644
--- a/stdlib/2/heapq.pyi
+++ b/stdlib/2/heapq.pyi
@@ -14,3 +14,4 @@ def heapreplace(heap: List[_T], item: _T) -> _T: ...
 def merge(*iterables: Iterable[_T]) -> Iterable[_T]: ...
 def nlargest(n: int, iterable: Iterable[_T], key: Optional[Callable[[_T], _Sortable]] = ...) -> List[_T]: ...
 def nsmallest(n: int, iterable: Iterable[_T], key: Optional[Callable[[_T], _Sortable]] = ...) -> List[_T]: ...
+def _heapify_max(__x: List[_T]) -> None: ...  # undocumented
diff --git a/stdlib/3/heapq.pyi b/stdlib/3/heapq.pyi
index 391898f7c..42cbb1fd3 100644
--- a/stdlib/3/heapq.pyi
+++ b/stdlib/3/heapq.pyi
@@ -10,3 +10,4 @@ def heapreplace(__heap: List[_T], __item: _T) -> _T: ...
 def merge(*iterables: Iterable[_T], key: Optional[Callable[[_T], Any]] = ..., reverse: bool = ...) -> Iterable[_T]: ...
 def nlargest(n: int, iterable: Iterable[_T], key: Optional[Callable[[_T], Any]] = ...) -> List[_T]: ...
 def nsmallest(n: int, iterable: Iterable[_T], key: Optional[Callable[[_T], Any]] = ...) -> List[_T]: ...
+def _heapify_max(__x: List[_T]) -> None: ...  # undocumented