diff --git a/Lib/multiprocessing/managers.py b/Lib/multiprocessing/managers.py
index 11c6e21de90e693..03d7577bdd81657 100644
--- a/Lib/multiprocessing/managers.py
+++ b/Lib/multiprocessing/managers.py
@@ -1224,7 +1224,7 @@ def __isub__(self, value):
 
     __class_getitem__ = classmethod(types.GenericAlias)
 
-collections.abc.MutableMapping.register(_BaseSetProxy)
+collections.abc.MutableSet.register(_BaseSetProxy)
 
 
 ArrayProxy = MakeProxyType('ArrayProxy', (
diff --git a/Lib/test/_test_multiprocessing.py b/Lib/test/_test_multiprocessing.py
index e5f618f5f2e84f4..3958162eaa2e29d 100644
--- a/Lib/test/_test_multiprocessing.py
+++ b/Lib/test/_test_multiprocessing.py
@@ -2841,6 +2841,11 @@ def test_dict_proxy_nested(self):
         self.assertIsInstance(outer[0], list)  # Not a ListProxy
         self.assertEqual(outer[-1][-1]['feed'], 3)
 
+    def test_set_isinstance(self):
+        s = self.set()
+        self.assertIsInstance(s, collections.abc.MutableSet)
+        self.assertNotIsInstance(s, collections.abc.MutableMapping)
+
     def test_nested_queue(self):
         a = self.list() # Test queue inside list
         a.append(self.Queue())
@@ -7675,6 +7680,7 @@ class ManagerMixin(BaseMixin):
     Array = property(operator.attrgetter('manager.Array'))
     list = property(operator.attrgetter('manager.list'))
     dict = property(operator.attrgetter('manager.dict'))
+    set = property(operator.attrgetter('manager.set'))
     Namespace = property(operator.attrgetter('manager.Namespace'))
 
     @classmethod
diff --git a/Misc/NEWS.d/next/Library/2025-12-18-10-37-01.gh-issue-142740.Di48Rf.rst b/Misc/NEWS.d/next/Library/2025-12-18-10-37-01.gh-issue-142740.Di48Rf.rst
new file mode 100644
index 000000000000000..389704bc9288263
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-12-18-10-37-01.gh-issue-142740.Di48Rf.rst
@@ -0,0 +1,3 @@
+Register :class:`!multiprocessing.managers.SetProxy` as
+:class:`collections.abc.MutableSet` rather than
+:class:`~collections.abc.MutableMapping`.