diff -r b78574cb00ab Objects/unicodeobject.c
--- a/Objects/unicodeobject.c	Tue Nov 08 22:53:59 2016 -0500
+++ b/Objects/unicodeobject.c	Wed Nov 09 23:36:26 2016 +0800
@@ -5101,7 +5101,7 @@
 #if SIZEOF_WCHAR_T == 4
             assert(0);
 #else
-            assert(Py_UNICODE_IS_SURROGATE(ch));
+            assert(ch > 0xFFFF && ch <= MAX_UNICODE);
             /*  compute and append the two surrogates: */
             unicode[outpos++] = (wchar_t)Py_UNICODE_HIGH_SURROGATE(ch);
             unicode[outpos++] = (wchar_t)Py_UNICODE_LOW_SURROGATE(ch);