diff -r 1be8cd7cee92 Objects/unicodeobject.c
--- a/Objects/unicodeobject.c	Sun Oct 09 15:37:43 2016 +0300
+++ b/Objects/unicodeobject.c	Sun Oct 09 23:41:36 2016 +0800
@@ -2113,6 +2113,11 @@
 {
     const unsigned char *s = (const unsigned char *)buffer;
     PyObject *unicode;
+
+    assert(size >= 0);
+    if (size == 0) {
+        _Py_RETURN_UNICODE_EMPTY();
+    }
     if (size == 1) {
 #ifdef Py_DEBUG
         assert((unsigned char)s[0] < 128);