#1492704: Ensure and document backward compatibility of the change
diff --git a/Doc/library/shutil.rst b/Doc/library/shutil.rst
index ec8cad2..b2efcbd 100644
--- a/Doc/library/shutil.rst
+++ b/Doc/library/shutil.rst
@@ -70,7 +70,8 @@
       Now returns *dst*.
 
    .. versionchanged:: 3.4
-      Raise :exc:`SameFileError` instead of :exc:`Error`.
+      Raise :exc:`SameFileError` instead of :exc:`Error`.  Since the former is
+      a subclass of the latter, this change is backward compatible.
 
 
 .. exception:: SameFileError