diff --git a/Doc/library/datetime.rst b/Doc/library/datetime.rst
index dae0dd7aa55898..196aa84473f135 100644
--- a/Doc/library/datetime.rst
+++ b/Doc/library/datetime.rst
@@ -2431,7 +2431,8 @@ incomplete or ambiguous ISO 8601 directives will raise a :exc:`ValueError`.
 The full set of format codes supported varies across platforms, because Python
 calls the platform C library's :func:`strftime` function, and platform
 variations are common. To see the full set of format codes supported on your
-platform, consult the :manpage:`strftime(3)` documentation.
+platform, consult the :manpage:`strftime(3)` documentation. There are also
+differences between platforms in handling of unsupported format specifiers.
 
 .. versionadded:: 3.6
    ``%G``, ``%u`` and ``%V`` were added.