Fix compiler warning.
diff --git a/Modules/_ctypes/_ctypes.c b/Modules/_ctypes/_ctypes.c
index cce986d..5b2a054 100644
--- a/Modules/_ctypes/_ctypes.c
+++ b/Modules/_ctypes/_ctypes.c
@@ -477,7 +477,7 @@
 static PyObject *
 CDataType_from_buffer_copy(PyObject *type, PyObject *args)
 {
-	void *buffer;
+	const void *buffer;
 	Py_ssize_t buffer_len;
 	Py_ssize_t offset = 0;
 	PyObject *obj, *result;