diff -r 58ebfa7c1361 Lib/test/test_descr.py
--- a/Lib/test/test_descr.py	Mon Feb 15 16:51:24 2016 +1100
+++ b/Lib/test/test_descr.py	Wed Feb 24 14:46:46 2016 +0100
@@ -396,6 +396,25 @@ class OperatorsTest(unittest.TestCase):
         a.setstate(100)
         self.assertEqual(a.getstate(), 100)
 
+    @test_support.precisionbigmemtest(2**31+5, 1)
+    def test_wrap_lenfunc_overflow(self, maxsize):
+        # Issue #26423: check for integer overflow in wrap_lenfunc()
+        # for length larger than 2^31 bytes (2 GB)
+        try:
+            data = b'x' * maxsize
+
+            # call wrap_lenfunc()
+            data_len = data.__len__()
+            self.assertEqual(data_len, maxsize)
+
+            # try also directly len(obj), just in case
+            self.assertEqual(len(data), maxsize)
+        finally:
+            # Ensure that memory is released
+            data = None
+            test_support.gc_collect()
+
+
 class ClassPropertiesAndMethods(unittest.TestCase):
 
     def assertHasAttr(self, obj, name):
diff -r 58ebfa7c1361 Objects/typeobject.c
--- a/Objects/typeobject.c	Mon Feb 15 16:51:24 2016 +1100
+++ b/Objects/typeobject.c	Wed Feb 24 14:46:46 2016 +0100
@@ -4303,7 +4303,7 @@ wrap_lenfunc(PyObject *self, PyObject *a
     res = (*func)(self);
     if (res == -1 && PyErr_Occurred())
         return NULL;
-    return PyInt_FromLong((long)res);
+    return PyInt_FromSsize_t(res);
 }
 
 static PyObject *