#4478: document that copyfile() can raise Error.
diff --git a/Doc/library/shutil.rst b/Doc/library/shutil.rst
index 944b9f1..b409bb7 100644
--- a/Doc/library/shutil.rst
+++ b/Doc/library/shutil.rst
@@ -43,7 +43,8 @@
Copy the contents (no metadata) of the file named *src* to a file named *dst*.
*dst* must be the complete target file name; look at :func:`copy` for a copy that
- accepts a target directory path.
+ accepts a target directory path. If *src* and *dst* are the same files,
+ :exc:`Error` is raised.
The destination location must be writable; otherwise, an :exc:`IOError` exception
will be raised. If *dst* already exists, it will be replaced. Special files
such as character or block devices and pipes cannot be copied with this