diff -r 40a1652349e9 Lib/test/test_itertools.py
--- a/Lib/test/test_itertools.py	Sun Oct 14 22:16:27 2012 +0200
+++ b/Lib/test/test_itertools.py	Mon Oct 15 09:50:50 2012 +0300
@@ -1267,6 +1267,14 @@
         self.pickletest(a, compare=ans)
         self.pickletest(b, compare=ans)
 
+    # Issue 13454: Crash when deleting backward iterator from tee()
+    def test_tee_del_backward(self):
+        forward, backward = tee(range(20000000))
+        for i in forward:
+            pass
+
+        del backward
+
     def test_StopIteration(self):
         self.assertRaises(StopIteration, next, zip())
 
diff -r 40a1652349e9 Modules/itertoolsmodule.c
--- a/Modules/itertoolsmodule.c	Sun Oct 14 22:16:27 2012 +0200
+++ b/Modules/itertoolsmodule.c	Mon Oct 15 09:50:50 2012 +0300
@@ -473,6 +473,19 @@
     return 0;
 }
 
+static void
+teedataobject_safe_decref(PyObject *obj)
+{
+    while (obj && Py_TYPE(obj) == &teedataobject_type &&
+           Py_REFCNT(obj) == 1) {
+        PyObject *nextlink = ((teedataobject *)obj)->nextlink;
+        ((teedataobject *)obj)->nextlink = NULL;
+        Py_DECREF(obj);
+        obj = nextlink;
+    }
+    Py_XDECREF(obj);
+}
+
 static int
 teedataobject_clear(teedataobject *tdo)
 {
@@ -480,7 +493,8 @@
     Py_CLEAR(tdo->it);
     for (i=0 ; i<tdo->numread ; i++)
         Py_CLEAR(tdo->values[i]);
-    Py_CLEAR(tdo->nextlink);
+    teedataobject_safe_decref(tdo->nextlink);
+    tdo->nextlink = NULL;
     return 0;
 }
 
@@ -617,6 +631,8 @@
 
     if (to->index >= LINKCELLS) {
         link = teedataobject_jumplink(to->dataobj);
+        if (link == NULL)
+            return NULL;
         Py_DECREF(to->dataobj);
         to->dataobj = (teedataobject *)link;
         to->index = 0;