diff -r 09bd552999bf Lib/test/seq_tests.py
--- a/Lib/test/seq_tests.py	Sat May 16 22:13:27 2015 +0300
+++ b/Lib/test/seq_tests.py	Sun May 17 12:49:09 2015 +0300
@@ -85,6 +85,14 @@ def itermulti(seqn):
     'Test multiple tiers of iterators'
     return chain(map(lambda x:x, iterfunc(IterGen(Sequence(seqn)))))
 
+class LyingTuple(tuple):
+    def __iter__(self):
+        yield 1
+
+class LyingList(list):
+    def __iter__(self):
+        yield 1
+
 class CommonTest(unittest.TestCase):
     # The type to be tested
     type2test = None
@@ -131,6 +139,10 @@ class CommonTest(unittest.TestCase):
             self.assertRaises(TypeError, self.type2test, IterNoNext(s))
             self.assertRaises(ZeroDivisionError, self.type2test, IterGenExc(s))
 
+        # Issue #23757
+        self.assertEqual(self.type2test(LyingTuple((2,))), self.type2test((1,)))
+        self.assertEqual(self.type2test(LyingList([2])), self.type2test([1]))
+
     def test_truth(self):
         self.assertFalse(self.type2test())
         self.assertTrue(self.type2test([42]))
diff -r 09bd552999bf Objects/abstract.c
--- a/Objects/abstract.c	Sat May 16 22:13:27 2015 +0300
+++ b/Objects/abstract.c	Sun May 17 12:49:09 2015 +0300
@@ -1681,7 +1681,7 @@ PySequence_Tuple(PyObject *v)
         Py_INCREF(v);
         return v;
     }
-    if (PyList_Check(v))
+    if (PyList_CheckExact(v))
         return PyList_AsTuple(v);
 
     /* Get iterator. */