diff --git a/Lib/python/pyhead.swg b/Lib/python/pyhead.swg
index 98ffa8d63..2ce0fb194 100644
--- a/Lib/python/pyhead.swg
+++ b/Lib/python/pyhead.swg
@@ -9,6 +9,7 @@
 #define PyString_FromString(x) PyUnicode_FromString(x)
 #define PyString_Format(fmt, args)  PyUnicode_Format(fmt, args)
 #define PyString_AsString(str) PyBytes_AsString(str)
+#define PyString_Size(str) PyBytes_Size(str)	
 #define PyString_InternFromString(key) PyUnicode_InternFromString(key)
 #define Py_TPFLAGS_HAVE_CLASS Py_TPFLAGS_BASETYPE
 #define PyString_AS_STRING(x) PyUnicode_AS_STRING(x)