=== modified file 'Include/object.h'
--- Include/object.h	2008-06-09 04:58:54 +0000
+++ Include/object.h	2008-06-13 06:13:23 +0000
@@ -725,7 +725,16 @@
 	(*Py_TYPE(op)->tp_dealloc)((PyObject *)(op)))
 #endif /* !Py_TRACE_REFS */
 
+#ifdef Py_DEBUG
+PyAPI_FUNC(void) _Py_INCREF_SanityCheck(PyObject *);
+#define _Py_SANITY_CHECK_COMMA ,
+#else
+#define _Py_INCREF_SanityCheck(op)
+#define _Py_SANITY_CHECK_COMMA
+#endif /* !Py_DEBUG */
+
 #define Py_INCREF(op) (				\
+	_Py_INCREF_SanityCheck((PyObject *)(op)) _Py_SANITY_CHECK_COMMA \
 	_Py_INC_REFTOTAL  _Py_REF_DEBUG_COMMA	\
 	((PyObject*)(op))->ob_refcnt++)
 

=== modified file 'Objects/object.c'
--- Objects/object.c	2008-06-09 04:58:54 +0000
+++ Objects/object.c	2008-06-13 06:08:35 +0000
@@ -2019,6 +2019,8 @@
 #endif
 	if (op->ob_refcnt < 0)
 		Py_FatalError("UNREF negative refcnt");
+	if (op->_ob_prev == NULL || op->_ob_next == NULL)
+		Py_FatalError("UNREF cleared object");
 	if (op == &refchain ||
 	    op->_ob_prev->_ob_next != op || op->_ob_next->_ob_prev != op)
 		Py_FatalError("UNREF invalid object");
@@ -2105,6 +2107,18 @@
 #endif
 
 
+#ifdef Py_DEBUG
+void
+_Py_INCREF_SanityCheck(PyObject *op)
+{
+    if (op->ob_refcnt == 0)
+        Py_FatalError("INCREF of 0 refcnt");
+    else if (op->ob_refcnt < 0)
+        Py_FatalError("INCREF of negative refcnt");
+}
+#endif
+
+
 /* Hack to force loading of cobject.o */
 PyTypeObject *_Py_cobject_hack = &PyCObject_Type;