diff --git a/Lib/enum.py b/Lib/enum.py
index ca6aff6..bcf411c 100644
--- a/Lib/enum.py
+++ b/Lib/enum.py
@@ -1005,6 +1005,14 @@ def __format__(self, format_spec):
             val = str(self)
         # mix-in branch
         else:
+            import warnings
+            warnings.warn(
+                    "in 3.12 format() will use the enum member, not the enum member's value;\n"
+                    "use a format specifier, such as :d for an IntEnum member, to maintain"
+                    "the current display",
+                    DeprecationWarning,
+                    stacklevel=2,
+                    )
             cls = self._member_type_
             val = self._value_
         return cls.__format__(val, format_spec)
diff --git a/Lib/test/test_enum.py b/Lib/test/test_enum.py
index 4f28b80..983c54b 100644
--- a/Lib/test/test_enum.py
+++ b/Lib/test/test_enum.py
@@ -528,6 +528,14 @@ def __format__(self, spec):
         self.assertEqual(str(TestFloat.one), 'one')
         self.assertEqual('{}'.format(TestFloat.one), 'TestFloat success!')
 
+    @unittest.skipUnless(
+            sys.version_info[:2] < (3, 12),
+            'mixin-format now uses member instead of member.value',
+            )
+    def test_mixin_format_warning(self):
+        with self.assertWarns(DeprecationWarning):
+            self.assertEqual(f'{self.Grades.B}', '4')
+
     def assertFormatIsValue(self, spec, member):
         self.assertEqual(spec.format(member), spec.format(member.value))