diff --git a/stdlib/3/ipaddress.pyi b/stdlib/3/ipaddress.pyi
index 90a88b8ea..c475a8984 100644
--- a/stdlib/3/ipaddress.pyi
+++ b/stdlib/3/ipaddress.pyi
@@ -97,6 +97,8 @@ class _BaseNetwork(_IPAddressBase, Container, Iterable[_A], Generic[_A]):
     def with_netmask(self) -> str: ...
     @property
     def with_prefixlen(self) -> str: ...
+    @property
+    def hostmask(self) -> _A: ...
 
 class _BaseInterface(_BaseAddress, Generic[_A, _N]):
     hostmask: _A