diff -r 378bdb92e5b7 Lib/test/test_grammar.py
--- a/Lib/test/test_grammar.py	Thu Feb 13 22:53:42 2014 -0800
+++ b/Lib/test/test_grammar.py	Fri Feb 14 17:58:00 2014 -0500
@@ -314,6 +314,13 @@
         self.assertEqual(f.__annotations__,
                           {'b': 1, 'c': 2, 'e': 3, 'g': 6, 'h': 7, 'j': 9,
                            'k': 11, 'return': 12})
+        # Check for issue #20625 -- annotations mangling
+        class Spam:
+            def f(self, *, __kw:1):
+                pass
+        class Ham(Spam): pass
+        self.assertEquals(Spam.f.__annotations__, {'_Spam__kw': 1})
+        self.assertEquals(Ham.f.__annotations__, {'_Spam__kw': 1})
         # Check for SF Bug #1697248 - mixing decorators and a return annotation
         def null(x): return x
         @null
diff -r 378bdb92e5b7 Lib/test/test_inspect.py
--- a/Lib/test/test_inspect.py	Thu Feb 13 22:53:42 2014 -0800
+++ b/Lib/test/test_inspect.py	Fri Feb 14 17:58:00 2014 -0500
@@ -2390,6 +2390,22 @@
         self.assertEqual(sig.return_annotation, 42)
         self.assertEqual(sig, inspect.signature(test))
 
+    def test_signature_on_mangled_parameters(self):
+        class Spam:
+            def foo(self, __p1:1=2, *, __p2:2=3):
+                pass
+        class Ham(Spam):
+            pass
+
+        self.assertEqual(self.signature(Spam.foo),
+                         ((('self', ..., ..., "positional_or_keyword"),
+                           ('_Spam__p1', 2, 1, "positional_or_keyword"),
+                           ('_Spam__p2', 3, 2, "keyword_only")),
+                          ...))
+
+        self.assertEqual(self.signature(Spam.foo),
+                         self.signature(Ham.foo))
+
 
 class TestParameterObject(unittest.TestCase):
     def test_signature_parameter_kinds(self):
diff -r 378bdb92e5b7 Python/compile.c
--- a/Python/compile.c	Thu Feb 13 22:53:42 2014 -0800
+++ b/Python/compile.c	Fri Feb 14 17:58:00 2014 -0500
@@ -1533,8 +1533,14 @@
 {
     if (annotation) {
         VISIT(c, expr, annotation);
-        if (PyList_Append(names, id))
+        PyObject *mangled = _Py_Mangle(c->u->u_private, id);
+        if (!mangled)
             return -1;
+        if (PyList_Append(names, mangled) < 0) {
+            Py_DECREF(mangled);
+            return -1;
+        }
+        Py_DECREF(mangled);
     }
     return 0;
 }