diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index 60cbffa..29ca08c 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -553,10 +553,16 @@
     PyUnicodeObject *unicode;
 
     if (w == NULL) {
+        if (size == 0)
+            return PyUnicode_FromStringAndSize(NULL, 0);
 	PyErr_BadInternalCall();
 	return NULL;
     }
 
+    if (size == -1) {
+        size = wcslen(w);
+    }
+
     unicode = _PyUnicode_New(size);
     if (!unicode)
         return NULL;