Issue #4129: int -> Py_ssize_t documentation.
diff --git a/Doc/c-api/marshal.rst b/Doc/c-api/marshal.rst
index 5ecccc4..34a83f4 100644
--- a/Doc/c-api/marshal.rst
+++ b/Doc/c-api/marshal.rst
@@ -94,3 +94,7 @@
containing *len* bytes pointed to by *string*. On error, sets the
appropriate exception (:exc:`EOFError` or :exc:`TypeError`) and returns
*NULL*.
+
+ .. versionchanged:: 2.5
+ This function used an :ctype:`int` type for *len*. This might require
+ changes in your code for properly supporting 64-bit systems.