diff --git a/Lib/test/pickletester.py b/Lib/test/pickletester.py
index 4c301ad..21deaff 100644
--- a/Lib/test/pickletester.py
+++ b/Lib/test/pickletester.py
@@ -876,6 +876,22 @@
         d = self.dumps(x, 2)
         self.assertRaises(RuntimeError, self.loads, d)
 
+    def test_reduce_bad_iterator(self):
+        # Issue4176: crash when 4th and 5th items of __reduce__()
+        # are not iterators
+        class C(object):
+            def __reduce__(self):
+                # 4th item is not an iterator
+                return list, (), None, [], None
+        class D(object):
+            def __reduce__(self):
+                # 5th item is not an iterator
+                return dict, (), None, None, []
+
+        for proto in protocols:
+            self.assertRaises(pickle.PickleError, self.dumps, C(), proto)
+            self.assertRaises(pickle.PickleError, self.dumps, D(), proto)
+
 # Test classes for reduce_ex
 
 class REX_one(object):
diff --git a/Misc/NEWS b/Misc/NEWS
index b8d17c1..b06e4b6 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -15,6 +15,9 @@
 Core and Builtins
 -----------------
 
+- Issue #4176: Fixed a crash when pickling an object which ``__reduce__``
+  method does not return iterators for the 4th and 5th items.
+
 - Issue 3723: Fixed initialization of subinterpreters.
 
 - Issue #4213: The file system encoding is now normalized by the
diff --git a/Modules/_pickle.c b/Modules/_pickle.c
index 2b672a7..a689c33 100644
--- a/Modules/_pickle.c
+++ b/Modules/_pickle.c
@@ -1961,8 +1961,9 @@
     PyObject *callable;
     PyObject *argtup;
     PyObject *state = NULL;
-    PyObject *listitems = NULL;
-    PyObject *dictitems = NULL;
+    PyObject *listitems = Py_None;
+    PyObject *dictitems = Py_None;
+    Py_ssize_t size;
 
     int use_newobj = self->proto >= 2;
 
@@ -1970,27 +1971,48 @@
     const char build_op = BUILD;
     const char newobj_op = NEWOBJ;
 
+    size = PyTuple_Size(args);
+    if (size < 2 || size > 5) {
+        PyErr_SetString(PicklingError, "tuple returned by "
+                        "__reduce__ must contain 2 through 5 elements");
+        return -1;
+    }
+
     if (!PyArg_UnpackTuple(args, "save_reduce", 2, 5,
                            &callable, &argtup, &state, &listitems, &dictitems))
         return -1;
 
     if (!PyCallable_Check(callable)) {
-        PyErr_SetString(PicklingError,
-                        "first argument of save_reduce() must be callable");
+        PyErr_SetString(PicklingError, "first item of the tuple "
+                        "returned by __reduce__ must be callable");
         return -1;
     }
     if (!PyTuple_Check(argtup)) {
-        PyErr_SetString(PicklingError,
-                        "second argument of save_reduce() must be a tuple");
+        PyErr_SetString(PicklingError, "second item of the tuple "
+                        "returned by __reduce__ must be a tuple");
         return -1;
     }
 
     if (state == Py_None)
         state = NULL;
+
     if (listitems == Py_None)
         listitems = NULL;
+    else if (!PyIter_Check(listitems)) {
+        PyErr_Format(PicklingError, "Fourth element of tuple"
+                     "returned by __reduce__ must be an iterator, not %s",
+                     Py_TYPE(listitems)->tp_name);
+        return -1;
+    }
+
     if (dictitems == Py_None)
         dictitems = NULL;
+    else if (!PyIter_Check(dictitems)) {
+        PyErr_Format(PicklingError, "Fifth element of tuple"
+                     "returned by __reduce__ must be an iterator, not %s",
+                     Py_TYPE(dictitems)->tp_name);
+        return -1;
+    }
 
     /* Protocol 2 special case: if callable's name is __newobj__, use
        NEWOBJ. */
@@ -2309,16 +2331,6 @@
                         "__reduce__ must return a string or tuple");
         goto error;
     }
-    if (Py_SIZE(reduce_value) < 2 || Py_SIZE(reduce_value) > 5) {
-        PyErr_SetString(PicklingError, "tuple returned by __reduce__ "
-                        "must contain 2 through 5 elements");
-        goto error;
-    }
-    if (!PyTuple_Check(PyTuple_GET_ITEM(reduce_value, 1))) {
-        PyErr_SetString(PicklingError, "second item of the tuple "
-                        "returned by __reduce__ must be a tuple");
-        goto error;
-    }
 
     status = save_reduce(self, reduce_value, obj);