diff --git a/Lib/test/test_bool.py b/Lib/test/test_bool.py
index c5a1f1f..ed47037 100644
--- a/Lib/test/test_bool.py
+++ b/Lib/test/test_bool.py
@@ -344,6 +344,16 @@ class BoolTest(unittest.TestCase):
                 except (Exception) as e_len:
                     self.assertEqual(str(e_bool), str(e_len))
 
+    def test_len_overflow(self):
+        self.assertIs(bool(range(1 << 1000)), True)
+        class A:
+            def __len__(self):
+                return length
+        length = 1 << 1000
+        self.assertIs(bool(A()), True)
+        length = -1 << 1000
+        self.assertRaises(ValueError, bool, A())
+
     def test_blocked(self):
         class A:
             __bool__ = None
diff --git a/Misc/NEWS b/Misc/NEWS
index 651d175..7d85dd1 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -10,7 +10,10 @@ What's New in Python 3.7.0 alpha 1?
 Core and Builtins
 -----------------
 
-- bpo-12414: sys.getsizeof() on a code object now returns the sizes 
+- bpo-29840: bool() no longer raises OverflowError for objects without defined
+  __bool__ when __len__() returned a large integer or raised OverflowError.
+
+- bpo-12414: sys.getsizeof() on a code object now returns the sizes
   which includes the code struct and sizes of objects which it references.
   Patch by Dong-hee Na.
 
diff --git a/Objects/object.c b/Objects/object.c
index 2d79e2f..1084911 100644
--- a/Objects/object.c
+++ b/Objects/object.c
@@ -1313,26 +1313,35 @@ PyObject_GenericSetDict(PyObject *obj, PyObject *value, void *context)
 int
 PyObject_IsTrue(PyObject *v)
 {
-    Py_ssize_t res;
+    Py_ssize_t len;
     if (v == Py_True)
         return 1;
     if (v == Py_False)
         return 0;
     if (v == Py_None)
         return 0;
-    else if (v->ob_type->tp_as_number != NULL &&
-             v->ob_type->tp_as_number->nb_bool != NULL)
-        res = (*v->ob_type->tp_as_number->nb_bool)(v);
-    else if (v->ob_type->tp_as_mapping != NULL &&
-             v->ob_type->tp_as_mapping->mp_length != NULL)
-        res = (*v->ob_type->tp_as_mapping->mp_length)(v);
+    if (v->ob_type->tp_as_number != NULL &&
+        v->ob_type->tp_as_number->nb_bool != NULL)
+        return (*v->ob_type->tp_as_number->nb_bool)(v);
+
+    if (v->ob_type->tp_as_mapping != NULL &&
+        v->ob_type->tp_as_mapping->mp_length != NULL)
+        len = (*v->ob_type->tp_as_mapping->mp_length)(v);
     else if (v->ob_type->tp_as_sequence != NULL &&
              v->ob_type->tp_as_sequence->sq_length != NULL)
-        res = (*v->ob_type->tp_as_sequence->sq_length)(v);
+        len = (*v->ob_type->tp_as_sequence->sq_length)(v);
     else
         return 1;
-    /* if it is negative, it should be either -1 or -2 */
-    return (res > 0) ? 1 : Py_SAFE_DOWNCAST(res, Py_ssize_t, int);
+    if (len > 0)
+        return 1;
+    if (len == 0)
+        return 0;
+    assert(PyErr_Occurred());
+    if (PyErr_ExceptionMatches(PyExc_OverflowError)) {
+        PyErr_Clear();
+        return 1;
+    }
+    return -1;
 }
 
 /* equivalent of 'not v'