diff --git a/Include/bytesobject.h b/Include/bytesobject.h
index a649d39..f1e01d1 100644
--- a/Include/bytesobject.h
+++ b/Include/bytesobject.h
@@ -42,7 +42,7 @@
 
 /* Macros, trading safety for speed */
 #define PyBytes_AS_STRING(self) (assert(PyBytes_Check(self)),((PyBytesObject *)(self))->ob_bytes)
-#define PyBytes_GET_SIZE(self)  (assert(PyBytes_Check(self)),((PyBytesObject *)(self))->ob_size)
+#define PyBytes_GET_SIZE(self)  (assert(PyBytes_Check(self)),Py_Size(self))
 
 #ifdef __cplusplus
 }
diff --git a/Include/stringobject.h b/Include/stringobject.h
index 1d932ff..c6ae1a8 100644
--- a/Include/stringobject.h
+++ b/Include/stringobject.h
@@ -85,7 +85,7 @@
 
 /* Macro, trading safety for speed */
 #define PyString_AS_STRING(op) (assert(PyString_Check(op)),(((PyStringObject *)(op))->ob_sval))
-#define PyString_GET_SIZE(op)  (assert(PyString_Check(op)),(((PyStringObject *)(op))->ob_size))
+#define PyString_GET_SIZE(op)  (assert(PyString_Check(op)),Py_Size(op))
 
 /* _PyString_Join(sep, x) is like sep.join(x).  sep must be PyStringObject*,
    x must be an iterable object. */