diff -r c3cec0f77eff Objects/odictobject.c
--- a/Objects/odictobject.c	Tue Oct 20 18:22:36 2015 +0300
+++ b/Objects/odictobject.c	Thu Oct 22 11:59:17 2015 +0300
@@ -1716,7 +1716,12 @@ PyODict_SetItem(PyObject *od, PyObject *
     int res = PyDict_SetItem(od, key, value);
     if (res == 0) {
         res = _odict_add_new_node((PyODictObject *)od, key);
-        /* XXX Revert setting the value on the dict? */
+        if (res < 0) {
+            PyObject *exc, *val, *tb;
+            PyErr_Fetch(&exc, &val, &tb);
+            (void) PyDict_DelItem(od, key);
+            _PyErr_ChainExceptions(exc, val, tb);
+        }
     }
     return res;
 };