diff --git a/Include/abstract.h b/Include/abstract.h
index 4fb16d0..b953308 100644
--- a/Include/abstract.h
+++ b/Include/abstract.h
@@ -612,7 +612,8 @@
 	is an iterator, this returns itself. */
 
 #define PyIter_Check(obj) \
-    ((obj)->ob_type->tp_iternext != NULL)
+    ((obj)->ob_type->tp_iternext != NULL && \
+     (obj)->ob_type->tp_iternext != &_PyObject_NextNotImplemented)
 
      PyAPI_FUNC(PyObject *) PyIter_Next(PyObject *);
      /* Takes an iterator object and calls its tp_iternext slot,
diff --git a/Include/object.h b/Include/object.h
index 0d20ecc..f3fdbda 100644
--- a/Include/object.h
+++ b/Include/object.h
@@ -438,6 +438,7 @@
 PyAPI_FUNC(int) PyObject_HasAttr(PyObject *, PyObject *);
 PyAPI_FUNC(PyObject **) _PyObject_GetDictPtr(PyObject *);
 PyAPI_FUNC(PyObject *) PyObject_SelfIter(PyObject *);
+PyAPI_FUNC(PyObject *) _PyObject_NextNotImplemented(PyObject *);
 PyAPI_FUNC(PyObject *) PyObject_GenericGetAttr(PyObject *, PyObject *);
 PyAPI_FUNC(int) PyObject_GenericSetAttr(PyObject *,
 					      PyObject *, PyObject *);