diff --git a/reference/_mpy_shed/buffer_mp.pyi b/reference/_mpy_shed/buffer_mp.pyi
index a1e3846b2..5913c7db2 100644
--- a/reference/_mpy_shed/buffer_mp.pyi
+++ b/reference/_mpy_shed/buffer_mp.pyi
@@ -1,6 +1,9 @@
 from _typeshed import Incomplete, structseq, AnyStr_co
 from typing_extensions import TypeAlias, TypeVar
 from array import array
+from typing import Union
+
+Buffer : TypeAlias= Union[bytes, bytearray, memoryview]
 
 # ------------------------------------------------------------------------------------
 # TODO: need some to allow string to be passed in : uart_1.write("hello")