diff -r 78a3d3700233 Objects/unicodeobject.c
--- a/Objects/unicodeobject.c	Sun Jul 03 19:11:13 2016 -0400
+++ b/Objects/unicodeobject.c	Tue Jul 05 20:55:10 2016 +0900
@@ -15043,22 +15043,17 @@
        though the key is present in the dictionary,
        namely when this happens during a stack overflow. */
     Py_ALLOW_RECURSION
-    t = PyDict_GetItem(interned, s);
+    t = PyDict_SetDefault(interned, s, s);
     Py_END_ALLOW_RECURSION
-
-    if (t) {
+    if (t == NULL) {
+        PyErr_Clear();
+        return;
+    }
+    if (t != s) {
         Py_INCREF(t);
         Py_SETREF(*p, t);
         return;
     }
-
-    PyThreadState_GET()->recursion_critical = 1;
-    if (PyDict_SetItem(interned, s, s) < 0) {
-        PyErr_Clear();
-        PyThreadState_GET()->recursion_critical = 0;
-        return;
-    }
-    PyThreadState_GET()->recursion_critical = 0;
     /* The two references in interned are not counted by refcnt.
        The deallocator will take care of this */
     Py_REFCNT(s) -= 2;