--- a/Include/bytesobject.h	Mon Oct 31 08:31:13 2016 +0200
+++ b/Include/bytesobject.h	Mon Oct 31 14:28:19 2016 +0200
@@ -74,6 +74,11 @@ PyAPI_FUNC(PyObject*) _PyBytes_FromHex(
 PyAPI_FUNC(PyObject *) PyBytes_DecodeEscape(const char *, Py_ssize_t,
 						   const char *, Py_ssize_t,
 						   const char *);
+/* Helper for PyBytes_DecodeEscape that detects invalid escape chars. */
+PyAPI_FUNC(PyObject *) _PyBytes_DecodeEscape(const char *, Py_ssize_t,
+                                             const char *, Py_ssize_t,
+                                             const char *,
+                                             const char **);
 
 /* Macro, trading safety for speed */
 #ifndef Py_LIMITED_API