diff --git a/stdlib/collections/__init__.pyi b/stdlib/collections/__init__.pyi
index c5fe236db..3f4b5e965 100644
--- a/stdlib/collections/__init__.pyi
+++ b/stdlib/collections/__init__.pyi
@@ -380,6 +380,7 @@ class ChainMap(MutableMapping[_KT, _VT], Generic[_KT, _VT]):
     def __len__(self) -> int: ...
     def __contains__(self, key: object) -> bool: ...
     def __missing__(self, key: _KT) -> _VT: ...  # undocumented
+    def __bool__(self) -> bool: ...
     def setdefault(self, key: _KT, default: _VT = ...) -> _VT: ...
     @overload
     def pop(self, key: _KT) -> _VT: ...